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a) CH4 covalent bond and σ-bond hybridized orbital; b) C2H6 covalent bond; c) C2H4 covalent bond, σ-bond in hybridized orbital, π-bond as hybridized orbitals; d) C2H2 covalent bond, σ-bond hybridized orbital.
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Additive manufacturing is an emerging and promising technology in biomedical, automotive, avionic and electronic industries, allowing advantages in terms of cost, weight reduction and efficiency upscaling respect to traditional manufacturing.
3D printing technologies offer high degree of freedom to customize products and incorporate components suc...
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Context 1
... understand why semiconducting polymers [6] , such as conjugated polymers, exhibit intriguing conductivity characteristics, it is necessary to understand how polymers bind. The majority of organic molecules, in particular CH₄ molecules, that is the chemical formula of methane, are composed of covalent bonds (Figure 3a). In this molecule the valence shell, which is the outermost one of a carbon four electrons are contained, while for hydrogen there is just one negative charge. ...
Context 2
... to the fact that carbon has four electrons, the CH4 molecule is constituted of four sigma bonds, differently angled due to electronic repulsion. Following considerations on the chemical structure of ethane, C2H6 (Figure 3b) assert it has a similar bonding structure to methane, each carbon is connected through three different σ-bonds to hydrogens and by another σ-bond to the other carbon and the structure is specular for the other carbon. When ethene or ethylene, C2H4, is introduced, the condition begins to improve (Figure 3c). ...
Context 3
... considerations on the chemical structure of ethane, C2H6 (Figure 3b) assert it has a similar bonding structure to methane, each carbon is connected through three different σ-bonds to hydrogens and by another σ-bond to the other carbon and the structure is specular for the other carbon. When ethene or ethylene, C2H4, is introduced, the condition begins to improve (Figure 3c). The carbon, as the other one, will still make with hydrogen a σ-bond. ...
Context 4
... the end through the overlapping of two pz orbitals a π-bond is formed (Figure 3c right). The electron-carrying link geometry, also called orbital, [7] starts to alter. ...
Context 5
... inside the molecule's sheet is contained the σ orbital and it is sandwiched between two atoms, the π orbital extends up and down the molecule's sheet. In the molecule of acetylene, C2H2, the number of π orbitals increases (Figure 3d), because the connection between carbon and hydrogen is unique, resulting in three unpaired electrons for each carbon atom, which creates with the other carbon one σ and two π hybrid orbitals, created through the orbital overlapping of a couple of pz with another couple of py. ...
Context 6
... indicated in Figure 29, the overall materials consist of amorphous domains and crystalline domains with a size range of ~10 nm. Charge transfer is faster along chains, moderate across chains and between lamellar planes is slower in such disordered materials (Figure 30) [90] . Additionally, the chains can be positioned arbitrarily along the x, y, or z axes. ...
Context 7
... the case of a two-atom primitive cell and therefore two orbitals per cell, as seen in Figure 33, two different transfer integrals, V1 and V2, must be considered. Due to the fact that the primitive cell has doubled in size, í µí± = 2í µí±, the new Brillouin zone has been half, with the new borders being ± í µí¼ 2í µí± ...
Context 8
... periodic potential of a conjugated polymer system is denoted by the SuSchrieffer-Heeger model, as shown in Figure 34. Electron energies inside the band gap (Eg) are banned, whereas electrons with energy above the gaps are permitted to conduct. ...
Context 9
... using the periodic boundary conditions and considering the polymer chain to be a circle with radius 'r', In this calculation, the total number of states is N = 2πr/a, where '2a' denotes the dimer's size or length. Thus, the density of states becomes as seen in Figure 35. Notably, only states satisfying |í µí°¸0µí°¸0 |> |í µí°¸íµí°¸í µí± | > |í µí°¸íµí°¸í µí± /2| are those an electron can be contained within. ...
Context 10
... a result, the CDW state is the ground state. Under these conditions, it is typical to observe the opening of a gap in the energy band at k = kF, as illustrated in Figure 36, as well as the Peierls transition. The Peierls instability and subsequent transition are observed in a wide variety of organic conductors, most notably those with charge transfer. ...
Context 11
... (also referred as kink solitons or bond-alternation defects) are topological defects that correspond to nonbonding 2pz orbitals populated by a single electron. These neutral solitons are important for charge transfer and hence conductivity, because they divide two segments of (CH)x with the same energy and travel along the chain ( Figure 37). Solitons arise in polyacetylene because the two domains A and B with opposing orientations of double bond alternation are degenerate and the energy cost of forming the soliton is less than the energy cost of band excitation. ...
Context 12
... soliton is a term that refers to non-bonding levels in the gap between the π* (conduction) and π (valence) bands. The neutral soliton has a spin of 1/2, while solitons with charges ±e have a spin equal to 0. As seen in Figure 38, doping allows for the creation of solitons with positive or negative charge, zero spin, as well as neutral solitons with spin 1/2 and even fractional charges. Solitons are delocalized over a large number of CH units and can freely travel along a chain without altering its form. ...
Context 13
... interchange of single and double bonds does not necessitate the provision of band gap energy for each monomer along the chain. The two radicals formed are a pair of soliton-antisoliton radicals that can travel apart along the chain, as seen in Figure 39. This process has no energy barrier, as electrons are believed to be delocalized. ...
Context 14
... size and energy of the polaron are dependent on the kind and degree of the lattice deformation produced. The molecular lattice deforms in three stages, as depicted in Figure 43, considering a molecule A that loses an electron as an example: ...
Context 15
... is a thermally activated quantum-mechanical tunnelling phenomenon in which charge carriers hop between monomers rather than traveling coherently ( Figure 53). While it is unavoidable that band transport plays a role in charge transfer in both polymeric semiconductors and their small molecule organic equivalents, it is apparent that hopping processes contribute far more to carrier mobility. ...
Context 16
... should be emphasized that intrachain transport can also involve hopping, even for conjugated polymers. A kink or flaw in a conjugated polymer allows charge to flow from one end of the chain to the other without traveling the entire length of the chain (Figure 53a) [159] . Similarly, many non-conjugated materials have excellent semiconducting properties, with charge transfer occurring only via hopping. ...
Context 17
... many non-conjugated materials have excellent semiconducting properties, with charge transfer occurring only via hopping. PVK, or Poly(Vinyl Carbazole), is arguably the simplest example of a polymer in which only hopping transport occurs (Figure 53c) [160] . Transport in such a polymer can occur between neighbouring chains or along the same chain, either by hopping from one portion to the next as seen in Figure 53a, or it can occur along the chain, simulating coherent band transport. ...
Context 18
... or Poly(Vinyl Carbazole), is arguably the simplest example of a polymer in which only hopping transport occurs (Figure 53c) [160] . Transport in such a polymer can occur between neighbouring chains or along the same chain, either by hopping from one portion to the next as seen in Figure 53a, or it can occur along the chain, simulating coherent band transport. ...
Context 19
... charge carriers are confined in isolated impurities, then the controlled addition of sufficient impurity should allow charges to flow across impurities. PVK (Figure 53c) is an example of a polymer with a high ionization potential that relies heavily on hopping transport. Due to the high ionization potential, it requires a great deal of energy to remove an electron, which is essentially the situation for a polymer that exhibits hole transport. ...
Context 20
... an intermediate zone between ohmic and space charge-limited behaviour is also seen, which in literature is referred to as the trapped space charge region, as illustrated in Figure 63. Charge carriers trapping and detrapping mechanism govern transport, spatial and energetic distributions of charges in the polymer. ...
Context 21
... localized states capture free carriers and prevent them from participating in the charge transport process, therefore degrading the polymer electrical characteristics and hence the device performance [184] . The polymer exhibits trap free space charge limited current behaviour when the applied voltage exceeds the mean trap energy, as seen in Figure 63. (4) SCLC region (J α μV 2 ) [185] . ...
Context 22
... terminal-pair, also referred to as four probe impedance spectroscopy [216] was the principal investigation technique employed to characterize the frequency dependence of the electrical conductivity in PEGDA:PEDOT devices. This method allows to extract from the impedance, the dielectric permittivity of the material and to isolate in a frequency range the unique contributions of charge carriers to the overall conductivity in the convolutional spectrum, as reported in Figure 73. PEGDA:PEDOT polymer composites -High frequency applications Figure 73: Response dielectric permittivity spectrum to an external excitation timevarying electric field from kHz to visible frequencies [217] . ...
Context 23
... method allows to extract from the impedance, the dielectric permittivity of the material and to isolate in a frequency range the unique contributions of charge carriers to the overall conductivity in the convolutional spectrum, as reported in Figure 73. PEGDA:PEDOT polymer composites -High frequency applications Figure 73: Response dielectric permittivity spectrum to an external excitation timevarying electric field from kHz to visible frequencies [217] . ...
Context 24
... understand why semiconducting polymers [6] , such as conjugated polymers, exhibit intriguing conductivity characteristics, it is necessary to understand how polymers bind. The majority of organic molecules, in particular CH₄ molecules, that is the chemical formula of methane, are composed of covalent bonds (Figure 3a). In this molecule the valence shell, which is the outermost one of a carbon four electrons are contained, while for hydrogen there is just one negative charge. ...
Context 25
... to the fact that carbon has four electrons, the CH4 molecule is constituted of four sigma bonds, differently angled due to electronic repulsion. Following considerations on the chemical structure of ethane, C2H6 (Figure 3b) assert it has a similar bonding structure to methane, each carbon is connected through three different σ-bonds to hydrogens and by another σ-bond to the other carbon and the structure is specular for the other carbon. When ethene or ethylene, C2H4, is introduced, the condition begins to improve (Figure 3c). ...
Context 26
... considerations on the chemical structure of ethane, C2H6 (Figure 3b) assert it has a similar bonding structure to methane, each carbon is connected through three different σ-bonds to hydrogens and by another σ-bond to the other carbon and the structure is specular for the other carbon. When ethene or ethylene, C2H4, is introduced, the condition begins to improve (Figure 3c). The carbon, as the other one, will still make with hydrogen a σ-bond. ...
Context 27
... the end through the overlapping of two pz orbitals a π-bond is formed (Figure 3c right). The electron-carrying link geometry, also called orbital, [7] starts to alter. ...
Context 28
... inside the molecule's sheet is contained the σ orbital and it is sandwiched between two atoms, the π orbital extends up and down the molecule's sheet. In the molecule of acetylene, C2H2, the number of π orbitals increases (Figure 3d), because the connection between carbon and hydrogen is unique, resulting in three unpaired electrons for each carbon atom, which creates with the other carbon one σ and two π hybrid orbitals, created through the orbital overlapping of a couple of pz with another couple of py. ...
Context 29
... indicated in Figure 29, the overall materials consist of amorphous domains and crystalline domains with a size range of ~10 nm. Charge transfer is faster along chains, moderate across chains and between lamellar planes is slower in such disordered materials (Figure 30) [90] . Additionally, the chains can be positioned arbitrarily along the x, y, or z axes. ...
Context 30
... the case of a two-atom primitive cell and therefore two orbitals per cell, as seen in Figure 33, two different transfer integrals, V1 and V2, must be considered. Due to the fact that the primitive cell has doubled in size, í µí± = 2í µí±, the new Brillouin zone has been half, with the new borders being ± í µí¼ 2í µí± ...
Context 31
... periodic potential of a conjugated polymer system is denoted by the SuSchrieffer-Heeger model, as shown in Figure 34. Electron energies inside the band gap (Eg) are banned, whereas electrons with energy above the gaps are permitted to conduct. ...
Context 32
... using the periodic boundary conditions and considering the polymer chain to be a circle with radius 'r', In this calculation, the total number of states is N = 2πr/a, where '2a' denotes the dimer's size or length. Thus, the density of states becomes as seen in Figure 35. Notably, only states satisfying |í µí°¸0µí°¸0 |> |í µí°¸íµí°¸í µí± | > |í µí°¸íµí°¸í µí± /2| are those an electron can be contained within. ...
Context 33
... a result, the CDW state is the ground state. Under these conditions, it is typical to observe the opening of a gap in the energy band at k = kF, as illustrated in Figure 36, as well as the Peierls transition. The Peierls instability and subsequent transition are observed in a wide variety of organic conductors, most notably those with charge transfer. ...
Context 34
... (also referred as kink solitons or bond-alternation defects) are topological defects that correspond to nonbonding 2pz orbitals populated by a single electron. These neutral solitons are important for charge transfer and hence conductivity, because they divide two segments of (CH)x with the same energy and travel along the chain ( Figure 37). Solitons arise in polyacetylene because the two domains A and B with opposing orientations of double bond alternation are degenerate and the energy cost of forming the soliton is less than the energy cost of band excitation. ...
Context 35
... soliton is a term that refers to non-bonding levels in the gap between the π* (conduction) and π (valence) bands. The neutral soliton has a spin of 1/2, while solitons with charges ±e have a spin equal to 0. As seen in Figure 38, doping allows for the creation of solitons with positive or negative charge, zero spin, as well as neutral solitons with spin 1/2 and even fractional charges. Solitons are delocalized over a large number of CH units and can freely travel along a chain without altering its form. ...
Context 36
... interchange of single and double bonds does not necessitate the provision of band gap energy for each monomer along the chain. The two radicals formed are a pair of soliton-antisoliton radicals that can travel apart along the chain, as seen in Figure 39. This process has no energy barrier, as electrons are believed to be delocalized. ...
Context 37
... size and energy of the polaron are dependent on the kind and degree of the lattice deformation produced. The molecular lattice deforms in three stages, as depicted in Figure 43, considering a molecule A that loses an electron as an example: ...
Context 38
... is a thermally activated quantum-mechanical tunnelling phenomenon in which charge carriers hop between monomers rather than traveling coherently ( Figure 53). While it is unavoidable that band transport plays a role in charge transfer in both polymeric semiconductors and their small molecule organic equivalents, it is apparent that hopping processes contribute far more to carrier mobility. ...
Context 39
... should be emphasized that intrachain transport can also involve hopping, even for conjugated polymers. A kink or flaw in a conjugated polymer allows charge to flow from one end of the chain to the other without traveling the entire length of the chain (Figure 53a) [159] . Similarly, many non-conjugated materials have excellent semiconducting properties, with charge transfer occurring only via hopping. ...
Context 40
... many non-conjugated materials have excellent semiconducting properties, with charge transfer occurring only via hopping. PVK, or Poly(Vinyl Carbazole), is arguably the simplest example of a polymer in which only hopping transport occurs (Figure 53c) [160] . Transport in such a polymer can occur between neighbouring chains or along the same chain, either by hopping from one portion to the next as seen in Figure 53a, or it can occur along the chain, simulating coherent band transport. ...
Context 41
... or Poly(Vinyl Carbazole), is arguably the simplest example of a polymer in which only hopping transport occurs (Figure 53c) [160] . Transport in such a polymer can occur between neighbouring chains or along the same chain, either by hopping from one portion to the next as seen in Figure 53a, or it can occur along the chain, simulating coherent band transport. ...
Context 42
... charge carriers are confined in isolated impurities, then the controlled addition of sufficient impurity should allow charges to flow across impurities. PVK (Figure 53c) is an example of a polymer with a high ionization potential that relies heavily on hopping transport. Due to the high ionization potential, it requires a great deal of energy to remove an electron, which is essentially the situation for a polymer that exhibits hole transport. ...
Context 43
... an intermediate zone between ohmic and space charge-limited behaviour is also seen, which in literature is referred to as the trapped space charge region, as illustrated in Figure 63. Charge carriers trapping and detrapping mechanism govern transport, spatial and energetic distributions of charges in the polymer. ...
Context 44
... localized states capture free carriers and prevent them from participating in the charge transport process, therefore degrading the polymer electrical characteristics and hence the device performance [184] . The polymer exhibits trap free space charge limited current behaviour when the applied voltage exceeds the mean trap energy, as seen in Figure 63. (4) SCLC region (J α μV 2 ) [185] . ...
Context 45
... terminal-pair, also referred to as four probe impedance spectroscopy [216] was the principal investigation technique employed to characterize the frequency dependence of the electrical conductivity in PEGDA:PEDOT devices. This method allows to extract from the impedance, the dielectric permittivity of the material and to isolate in a frequency range the unique contributions of charge carriers to the overall conductivity in the convolutional spectrum, as reported in Figure 73. PEGDA:PEDOT polymer composites -High frequency applications Figure 73: Response dielectric permittivity spectrum to an external excitation timevarying electric field from kHz to visible frequencies [217] . ...
Context 46
... method allows to extract from the impedance, the dielectric permittivity of the material and to isolate in a frequency range the unique contributions of charge carriers to the overall conductivity in the convolutional spectrum, as reported in Figure 73. PEGDA:PEDOT polymer composites -High frequency applications Figure 73: Response dielectric permittivity spectrum to an external excitation timevarying electric field from kHz to visible frequencies [217] . ...
