Marcus Müller

Georg-August-Universität Göttingen | GAUG · Institute for Theoretical Physics

The free-energy landscape of self-assembling block copolymer systems is characterized by a multitude of metastable minima. Using particle-based simulations of a soft, coarse-grained model, we explore opportunities to reproducibly direct the spontaneous ordering of these self-assembling systems into a metastable complex network morphology-specifical...

The formation of an hourglass-shaped passage (stalk) connecting two apposed membranes is an essential initial step in membrane fusion. The most probable transition path from two separate membranes to a stalk, i.e., the minimum free-energy path (MFEP), is constructed using a combination of particle simulations and string method. For the reversible t...

Exposition of uni-lamellar vesicles to attractive surfaces is a frequently used way to create supported lipid bilayers. Although this approach is known to produce continuous supported bilayers, the mechanism of their formation and its dependence on factors like surface interaction and roughness or membrane tension as well as the interplay between n...

Division of intracellular organelles often correlates with additional membrane wrapping, e.g., by the endoplasmic reticulum or the outer mitochondrial membrane. Such wrapping plays a vital role in proteome and lipidome organization. However, how an extra membrane impacts the mechanics of the division has not been investigated. Here we combine fluor...

Vesicles on substrates play a fundamental role in many biological processes, ranging from neurotransmitter release at the synapse on small scales to the nutrient intake of trees by large vesicles. For these processes, the adsorption or desorption of vesicles to biological substrates is crucial. Consequently, it is important to understand the factor...

Conventional theories of weak polyelectrolytes are either computationally prohibitive to account for the multidimensional inhomogeneity of polymer ionization in a liquid environment or oversimplistic in describing the coupling effects of ion-explicit electrostatic interactions and long-range intrachain correlations. To bridge this gap, we implement...

Chemical reaction cycles are prototypical examples how to drive systems out of equilibrium and introduce novel, life-like properties into soft-matter systems. We report simulations of amphiphilic molecules in aqueous solution. The molecule's head group is permanently hydrophilic, whereas the reaction cycle switches the molecule's tail from hydrophi...

Block copolymer membranes offer a bottom-up approach to form isoporous membranes that are useful for ultrafiltration of functional macromolecules, colloids, and water purification. The fabrication of isoporous block copolymer membranes from a mixed film of an asymmetric block copolymer and two solvents involves two stages: First, the volatile solve...

The interactions between vesicle and substrate have been studied by simulation and experiment. We grafted polyacrylic acid brushes containing cysteine side chains at a defined area density on planar lipid membranes. Specular X-ray reflectivity data indicated that the addition of Cd2+ ions induces the compaction of the polymer brush layer and modula...

Highly coarse-grained (hCG) linear polymer models allow for accessing long time and length scales by dissipative particle dynamics (DPD). This top-down strategy exploits the universal equilibrium behavior of long, flexible macromolecules by accounting only for the relevant interactions, such as molecular connectivity, and by parametrizing their str...

A supercooled fluid close to the glass transition develops nonlocal shear stress correlations that anticipate the emergence of elasticity. We performed molecular dynamics simulations of a binary Lennard-Jones mixture at different temperatures and investigated the spatiotemporal autocorrelation function of the shear stressfor different wavevectors,...

We grafted polyacrylic acid brushes containing cysteine side chains at a defined surface density on planar lipid membranes. Specular X-ray reflectivity data indicated that the addition of Cd2+ ions induces the compaction of the polymer brush layer and modulates the adhesion of lipid vesicles. The critical threshold level inducing the switch from no...

Using analytical considerations and particle-based simulations of a coarse-grained model, we study the relaxation of a density modulation in a polymer system without nonbonded interactions. We demonstrate that shallow density modulations with identical amplitudes and wavevectors that have been prepared by different processes exhibit different nonex...

Using computer simulations and phenomenological considerations, we study the interplay between elasticity and microphase separation in quasi-two-dimensional phantom networks, obtained by cross-linking AB diblock copolymers at their ends. In the limit of weak stretching, where the average distance, lu, of A cross-links (or the mesh-cell size of the...

A new mesophase in binary blends of A–b–(BA′)3 miktoarm star block copolymers and A homopolymers has recently been discovered experimentally and explored with field-theoretic simulations. This mesophase has been reported to consist of aperiodic discrete domains of A embedded in a continuous matrix of B up to very high concentrations of A. Because o...

Using self-consistent field theory (SCFT) and Monte-Carlo simulations, we study the structure and dynamics of loops and bridges in the lamellar phase of symmetric ABA triblock copolymers at χN = 80. The bridge fraction, νB, linearly correlates with the average variance, X12 = ⟨X1i2⟩, of the first Rouse mode. Using SCFT with constraint X12, we calcu...

A concept of patternable top-coats dedicated to directed self-assembly of high-χ block copolymers is detailed, where the design enables a crosslinking reaction triggered by thermal or photo-activation. Nanostructured BCP areas with controlled domains orientation are selected through a straightforward top-coat lithography step with unique integratio...

Porous polymer and copolymer membranes are useful for ultrafiltration of functional macromolecules, colloids, and water purification. In particular, block copolymer membranes offer a bottom-up approach to form isoporous membranes. To optimize permeability, selectivity, longevity, and cost, and to rationally design fabrication processes, direct insi...

Small unilamellar vesicles (20–100 nm diameter) are model systems for strongly curved lipid membranes, in particular for cell organelles. Routinely, small-angle X-ray scattering (SAXS) is employed to study their size and electron-density profile (EDP). Current SAXS analysis of small unilamellar vesicles (SUVs) often employs a factorization into the...

The directed self-assembly (DSA) of block copolymers (BCPs) is a powerful method for the manufacture of high-resolution features. Critical issues remain to be addressed for successful implementation of DSA, such as dewetting and controlled orientation of BCP domains through physicochemical manipulations at the BCP interfaces, and the spatial positi...

A hierarchical (triple scale) simulation methodology is presented for the prediction of the dynamical and rheological properties of high molecular-weight entangled polymer melts. The methodology consists of atomistic, moderately coarse-grained (mCG), and highly coarse-grained slip-spring (SLSP) simulations. At the mCG level, a few chemically bonded...

Using molecular simulations of POPC lipids in conjunction with the calculation of the Minimum Free-Energy Path (MFEP), we study the effect of strong membrane curvature on the formation of the first fusion intermediate-the stalk between a vesicle and its periodic image. We find that the thermodynamic stability of this hourglass-shaped, hydrophobic c...

A hierarchical (triple scale) simulation methodology is presented for the prediction of the dynamical and rheological properties of high molecular weight entangled polymer melts. The methodology consists of atomistic, moderately coarse-grained (mCG), and highly coarse-grained slip-spring (SLSP) simulations. At the mCG level, a few chemically bonded...

We observe an anomalous liquid expansion after quenching a binary mixture at coexistence to low pressures in the vapor phase by numerical calculations. This evaporation-induced expansion can be attributed to the pressure imbalance near the liquid-vapor interface, which originates from the interplay between the complex thermodynamics of binary mixtu...

We study, by coarse-grained molecular dynamics simulations, equilibrium and flow properties of a liquid in cylindrical nanochannels, coated with polymer brushes. The parameters of the interaction potential model confer a chemical incompatibility between brush monomers and liquid particles. First, we study cylindrical channels whose radii are larger...

The morphology of a multicomponent polymer melt within selfconsistent field theory (SCFT) is completely characterized by the spatial density distribution of the components. SCFT therefore assumes that the molecular conformations are fast variables that adopt their equilibrium statistics with respect to a given density distribution. There are multipl...

We investigate the confinement-induced formation and stability of helix morphologies in lamella-forming AB diblock copolymers via large-scale, particle-based, single-chain-in-mean-field simulations. Such helix structures are rarely observed in bulk or thin films. Structure formation is induced by quenching incompatibility, χN, from a disordered mor...

In article number 2004922, Qiyun Tang, Kai Zhang, and co‐workers report Janus‐like films fabricated via the self‐assembly of surface‐acylated cellulose nanowhiskers (CNWs) with or without graphene oxide (GO). The obtained films with asymmetric topographies and properties on their top and bottom surfaces show different wettabilities and fast solvent...

The kinetics of forming multifunctional nanostructures, such as nanotheranostic superstructures, is often highly protracted, involving macroscopic time scales and resulting in nanostructures that correspond to kinetically stable states rather than thermodynamic equilibrium. Predicting such kinetically stable nanostructures becomes a great challenge...

For the first time Janus‐like films of surface‐acylated cellulose nanowhiskers (CNWs) with or without graphene oxide (GO) via one‐step evaporation‐driven self‐assembly process are reported, which have reconstructible time‐dependent micro‐/nanostructures and asymmetric wettability. The heterogeneous aggregation of CNWs on rough Teflon substrates fav...

Synapses play a central role for the processing of information in the brain and have been analyzed in countless biochemical, electrophysiological, imaging, and computational studies. The functionality and plasticity of synapses are nevertheless still difficult to predict, and conflicting hypotheses have been proposed for many synaptic processes. In...

We introduce a computationally efficient continuum technique to simulate the complex kinetic pathways of block copolymer self-assembly. Subdiffusive chain dynamics is taken into account via nonlocal Onsager coefficients. An application to directed self-assembly (DSA) of thin films of diblock copolymers on patterned substrates reveals the conditions...

Graphene-based nanostructured systems and van-der-Waals heterostructures comprise a material class of growing technological and scientific importance. Joining materials with vastly different properties, polymer-graphene heterosystems promise diverse applications in surface- and nanotechnology, including photovoltaics or nanotribology. Fundamentally...

Process-directed self-assembly refers to processes that reproducibly trap the kinetics of structure formation that ensues after a sudden change (“quench”) of the thermodynamic state into a desired, (meta)stable target state. This strategy benefits from specific advantages of copolymer systems, such as the rather comprehensive knowledge of equilibri...

We demonstrate by molecular simulations that the Ostwald ripening of crystalline polymer nuclei within the fast-evaporation-induced 2D skin layer is retarded at suitable temperatures and evaporation rates. Such an anomalous ripening can be attributed to the interplay between the thermodynamically driven diffusion of noncrystalline fragments toward...

Using large-scale simulations with the graphics processing unit (GPU) accelerated Highly Optimized Object-oriented Many-particle Dynamics (HOOMD)-blue software we investigate the anisotropic, dynamic-mechanical properties of lamellae-forming diblock copolymer melts. Both, the shear-stress autocorrelation function in equilibrium as well as stress-co...

On short length and time scales, the collective kinetics of relaxation or structure formation in multicomponent polymer melts, such as homopolymer blends and copolymers, is influenced by the subdiffusive single-chain dynamics. We compare the predictions of the dynamic random-phase approximation (D-RPA) and dynamic self-consistent field theory (D-SC...

Various types of devices require hierarchically nano-patterned substrates, where spacing between patterned domains is controlled. Ultra-confined films exhibit extreme morphological sensitivity to slight variations in film thickness when the substrate is highly selective toward one of the blocks. Here, it is shown that using the substrate’s topograp...

Conditions of rapid processing often drive polymers to adopt nonequilibrium molecular conformations, which, in turn, can give rise to structural, dynamical, and mechanical properties that are significantly different from those in thermodynamic equilibrium. However, despite the possibility to control the desired nonequilibrium properties of polymers...

In equilibrium the interface potential that describes the interaction between two AB interfaces in a binary blend of A and B homopolymers is attractive at all distances, resulting in coarsening of the blend morphology even in the absence of interface curvature. We demonstrate that the dissipative assembly in response to a time-periodic variation of...

In equilibrium the interface potential that describes the interaction between two AB interfaces ina binary blend of A and B homopolymers is attractive at all distances, resulting in coarsening of theblend morphology even in the absence of interface curvature. We demonstrate that the dissipativeassembly in response to a time-periodic variation of th...

Diblock copolymers play an important role in the fabrication of battery materials and fuel cells. For these applications, one block provides mechanical stability, whereas the other is conducting. The application characteristics of the material critically depend on the morphology of the multicomponent material, and three-dimensional, percolating dom...

Significance The isolated transmembrane domains (TMDs) of fusion proteins such as SNARE molecules drastically lower the free energy of both the stalk barrier and metastable stalk, which is not trivially explained by molecular shape arguments. The here-demonstrated methodology may have far-reaching applications in the fields of medicine and pharmaco...

High density and high resolution line and space patterns on surfaces are obtained by directed self-assembly of lamella-forming block copolymers using wide-stripes chemical guiding patterns. When the width of the chemical pattern is larger than the half-pitch of the block copolymer, the interaction energy between each block copolymer domain and the...

Mesoporous crystalline (hydr)oxides of low-valence metal ions (M(II) and M(III)) are highly demanded in the context of various applications. In this study, we demonstrate key factors to the successful formation of ordered mesoporous films through the Assembly of Nano-Building Block (ANBB) approach using a colloidal solution of crystalline M(OH)2 (M...

Besides dictating the equilibrium phase diagram, the rugged free-energy landscape of AB block copolymers gives rise to a multitude of non-equilibrium phenomena. Self-consistent field theory (SCFT) can be employed to calculate the mean-field free energy, F[ϕAtarget], of a non-equilibrium unstable state that is characterized by a given spatial densit...

This article aims to stimulate research on non‐equilibrium macromolecular systems, as nowadays a large toolbox to synthesize tailored macromolecules is available. A large variety of characterization methods covering a broad spectrum of length and timescales allows researchers to follow and also manipulate macromolecular systems on their paths towar...

A step-shear deformation imparts an instantaneous, anisotropic stimulus onto a microphase-separated block copolymer mesophase. In response to the concomitant molecular stretching and collective deformation of the morphology, the system relaxes toward a long-lived, pseudometastable state with a minuscule residual shear stress. Using molecular simula...

Using computer simulation of a coarse-grained, bead–spring model as well as scanning-probe microscopy of polytBA brushes in ethanol, we demonstrate that upon compression a poor solvent between two apposing polymer brushes does not remain a uniform thin film but, instead, forms a lateral, nanoscopic structure. The characteristic lateral length scale...

Shear flow is a versatile strategy to align microphase-separated morphologies of diblock copolymers over macroscopic scales. Details of the local mechanism of reorientation toward the steady, nonequilibrium state, however, are only incompletely understood. Using large scale molecular simulation as well as experiments, we study the shear-alignment m...

In equilibrium, copolymers self-assemble into spatially modulated phases with long-range order. When the system is quenched far below the order-disorder transition temperature, however, such an idealized, defect-free structure is difficult to obtain in experiments and simulations, instead a fingerprint-like structure forms. The relaxation toward lo...

The preparation of nanoparticles and their targeted connection with other functional units is one key challenge in developing nanoscale devices. Herein, we report an experimental strategy toward the development of anisotropic nanoparticle architectures. Our approach is based on phase separation of binary mixed polymer brushes on gold nanoparticle s...

Synthetic polymers, nanoparticles, and carbon-based materials have great potential in applications including drug delivery, gene transfection, in vitro and in vivo imaging, and the alteration of biological function. Nature and humans use different design strategies to create nanomaterials: biological objects have emerged from billions of years of e...

The formation and closure of aqueous pores in lipid bilayers is a key step in various biophysical processes. Large pores are well described by classical nucleation theory, but the free-energy landscape of small, biologically relevant pores has remained largely unexplored. The existence of small and metastable “prepores” was hypothesized decades ago...

The purpose of this study is the development of phase-separating diblock copolymer model systems suitable for the comparison between the orientation process under shear and computer simulations of the same process. To do so, the polymer systems have to fulfill certain requirements like similar dynamics of both polymer blocks, which are associated w...

Coarse-grained models of polymer and biomolecular systems have enabled the computational study of cooperative phenomena, e.g., self-assembly, by lumping multiple atomistic degrees of freedom along the backbone of a polymer, lipid, or DNA molecule into one effective coarse-grained interaction center. Such a coarse-graining strategy leaves the number...

A microscopic molecular model of polymeric molecules that captures the effects of topological constraints is used to consider how microphase segregation can alter the distribution of entanglements both in space and along chain contours. Such topological constraints are obtained by using the Z1 algorithm, and it is found that for diblock copolymers...

The computational description of directed self-assembly (DSA) of copolymer materials requires the prediction of large-scale structure formation of copolymer materials guided by chemical or topographical patterns. The disparity between the periodicity of self-assembled structures and the large length scale of devices poses computational challenges t...

Ellipsoids have attracted abiding attention because of their shape-dependent, anisotropic properties. In some applications, e.g., photonic crystals, both positional and orientational order of the ellipsoidal packing are required. We propose a versatile, facile, and efficient strategy to fabricate positionally and orientationally ordered crystals of...

Via computer simulation of a coarse-grained model of two-component lipid bilayers, we compare two methods of measuring the intrinsic curvatures of the constituting monolayers. The first one is a generalization of the swelling method that, in addition to the assumption that the spontaneous curvature linearly depends on the composition of the lipid m...

Multi-component polymer systems are important for the development of new materials because of their ability to phase-separate or self-assemble into nano-structures. The Single-Chain-in-Mean-Field (SCMF) algorithm in conjunction with a soft, coarse-grained polymer model is an established technique to investigate these soft-matter systems. Here we pr...

Ordered mesostructured TiO2 thin films are employed in diverse applications ranging from catalysis and sensing, to photovoltaic and lithium-ion batteries. Experimentally these mesostructured thin films are fabricated via a sol-gel process coupled with evaporation-induced self-assembly of a supramolecular template, where the concentration of hydroge...

Membrane fission is a fundamental process in cells, involved inter alia in endocytosis, intracellular trafficking, and virus infection. Its underlying molecular mechanism, however, is only incompletely understood. Recently, experiments and computer simulation studies have revealed that dynamin-mediated membrane fission is a two-step process that pr...

Using self-consistent field theory (SCFT), we develop an accurate, local expression for the stress profiles in membranes and soft matter interfaces, in general. The bond stresses are expressed in terms of pre-computed chain propagators, which are used to describe the statistical weight of the molecules and therefore require minimal additional calcu...

Process-directed self-assembly of block copolymers refers to thermodynamic processes that reproducibly direct the kinetics of structure formation from a starting, unstable state into a selected, metastable mesostructure. We investigate the kinetics of self-assembly of linear ACB triblock copolymers after a rapid transformation of the middle C block...

Planet–satellite nanostructures from RAFT star polymers and larger (planet) as well as smaller (satellite) gold nanoparticles are analyzed in experiments and computer simulations regarding the influence of arm number of star polymers. A uniform scaling behavior of planet–satellite distances as a function of arm length was found both in the dried st...

Coarse grained simulation approaches provide powerful tools for the prediction of the equilibrium properties of polymeric systems. Recent efforts have sought to develop coarse-graining strategies capable of predicting the non-equilibrium behavior of entangled polymeric materials. Slip-link and slip-spring models, in particular, have been shown to b...

We report computer simulation of the self-assembly of alkylthiols on the surface of liquid mercury. Here we focus mainly on the alkylthiol behavior on mercury as a function of the surfactant surface coverage, which we study by means of large-scale Molecular Dynamics simulations of the equilibrium structure at room temperature. The majority of the p...

We study the kinetics of alignment and registration of block copolymers in an inhomogeneous electric field by computer simulations of a soft, coarse-grained model. The two blocks of the symmetric diblock copolymers are characterized by different dielectric constants. First, we demonstrate that a combination of graphoepitaxy and a homogeneous electr...

Structural properties of brushes which are composed of weak acidic and basic polyelectrolytes are studied in the framework of a particle-based approach that implicitly accounts for the solvent quality. Using a semi-grandcanonical partition function in the framework of the Single-Chain-in-Mean-Field (SCMF) algorithm, the weak polyelectrolyte is conc...

Graphene-based nanostructured systems and van-der-Waals heterostructures comprise a material class of growing technological and scientific importance. Joining materials with vastly different properties, polymer-graphene heterosystems promise diverse applications in surface- and nanotechnology, including photovoltaics or nanotribology. Fundamentally...

The thermodynamics of dislocations in thin films of lamella-forming diblock copolymers and their climb and glide motions are investigated using single-chain-in-mean-field (SCMF) simulations and self-consistent field theory (SCFT) in conjunction with the string method. The glide motion of a defect perpendicular to the stripe pattern is characterized...

A new methodology and the corresponding C++ code for mesoscopic simulations of elastomers are presented. The test system, crosslinked ds-1'4-polyisoprene' is simulated with a Brownian Dynamics/kinetic Monte Carlo algorithm as a dense liquid of soft, coarse-grained beads, each representing 5-10 Kuhn segments. From the thermodynamic point of view, th...

Molecular dynamics simulations of a coarse-grained model with soft, nonbonded interactions and implicit solvent are used to study the temperature- and pH-sensitive response of mixed brushes composed of poly(N-isopropylacrylamide) [PNIPAm] and poly(acrylic acid) [PAA] polymers. The model is developed in order to address experimentally relevant, larg...

Using computer simulation of a soft, coarse-grained model and self-consistent field theory we investigate how collapsed, globular chain conformations in the initial stages of structure formation, which are produced by spray-coating, affect the single-chain structure and morphology of microphase-separated multiblock copolymers. Comparing spray-coate...

Coarse-graining decimates degrees of freedom (DoFs), and the free-energy of the integrated-out DoF can be accounted for by endowing each of the coarse-grained particles with an internal energy and concomitant entropy. These eDPD models allow to study energy transport, however, the first-order integration scheme for the corresponding stochastic equa...

A technique is presented which maps the parameters of a bead spring model, using the Flory Huggins theory, to a specific experimental system. By keeping only necessary details, for the description of these systems, the mapping procedure turns into an estimation of a few characteristic parameters. An asset of this technique is that it is simple to a...

Self-assembled organic films on liquid metals feature a very rich phase behavior, which qualitatively differs from the one on crystalline metals. In contrast to conventional crystalline supports, self-assembled alkylthiol monolayers on liquid metals possess a considerably higher degree of molecular order, thus, enabling much robuster metal-molecule...

The introduction of DSA for lithography is still obstructed by a number of technical issues including the lack of a comprehensive computational platform. This work presents a direct source/mask/DSA optimization (SMDSAO) method, which incorporates standard lithographic metrics and figures of merit such as the maximization of process windows. The pro...

This article briefly summarizes some key theoretical concepts about phase transformations, discusses the extent, to which they differ from related phenomena in other materials, and mentions a few typical experiments to introduce the main techniques used to study such phase transitions. Phase transformations of polymeric materials, such as unmixing...

Various molecules are known to form self-assembled monolayers (SAMs) on the surface of liquids. We present a simple method of investigating the kinetics of such SAM formation on sessile drops of various liquids such as mercury, water and fluorocarbon. To measure the surface tension of the drops we used an optical tensiometer that calculates the sur...

The free-energy change of membrane shape transformations can be small, e.g., as in the case of membrane bending. Therefore, the calculation of the free-energy difference between different membrane morphologies is a challenge. Here, we discuss a computational method - field-theoretic umbrella sampling - to compute the local chemical potential of a n...

Using simulation and numerical self-consistent field theory of an unentangled diblock copolymer melt, we study the interplay between relaxation of molecular conformations from a highly stretched, nonequilibrium state and structure formation of the local, conserved density during self-assembly from a disordered state. We observe that the planar elon...

Patterning strategies based on directed self-assembly (DSA) of block copolymers, as one of the most appealing next-generation lithography techniques, have attracted abiding interest. DSA aims at fabricating defect-free geometrically simple patterns on large scales or irregular device-oriented structures. Successful application of DSA requires to co...

Significance A molecular model is used to calculate the free energy of formation of ordered and disordered copolymer morphologies. We rely on advanced methodologies to identify the minimum free energy pathways that connect such states of the material. Our predictions for defect formation and annealing are compared with experimental observations. Ou...

Chemically patterned surfaces have been successfully employed to direct the kinetics of self-assembly of block copolymers into dense, periodic morphologies (”chemoepitaxy”). Significant efforts have been directed towards understanding the kinetics of structure formation and, particularly, the formation and annihilation of defects. In the present ma...

Using particle-based simulation of a soft, coarse-grained model and self-consistent field theory (SCFT), we investigate the properties of dense living polymer systems with ring formation both in the bulk and in thin films. In the bulk, our results confirm that the molecular weight distribution of ring polymers exhibits a combination of an exponenti...