Filler surface adsorption of mesogenic epoxy for LC Epoxy/MgO composites with high thermal conductivity

Ota, Saki; Harada, Miyuki

doi:10.1016/j.jcomc.2020.100087

Cited by 8 publications

(9 citation statements)

References 23 publications

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“…LC epoxy−MgO composites increased the TC by adsorbing mesogenic epoxy units onto amine-modified MgO particle surfaces. 35 However, this increase in TC was ascribed to a well-ordered smectic structure in the epoxy matrix that characteristically developed in the composites comprising mesogenic epoxy-adsorbed MgO particles.…”

Section: Grafting Pthe5b3 On Mgopsmentioning

confidence: 99%

Thermal Conductivity Enhancement of Liquid Crystal Polymer–Solid Particle Composites by Grafting a Main-Chain-Type Liquid Crystal Polymer onto Particle Surfaces

Ishikawa

Kawahara

Tomizawa

et al. 2022

ACS Appl. Polym. Mater.

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Thermally conductive composites comprising filler particles dispersed in a polymer matrix can effectively enhance the thermal conductivity (TC) by increasing the TC of the matrix; however, the TCs of polymers are difficult to increase. This study demonstrates that a liquid crystal polymer (LCP) that forms the matrix of a composite increases the TC to the value that is measured along the liquid crystal (LC) director orientation (λ // ). The LCP used here comprised a thiol−ene-type monomer that enabled grafting of the main-chain-type LCP onto allyl-functionalized magnesium oxide particles (MgOPs) with a diameter of 10 μm. The mixtures of LCP-grafted MgOPs and the LCP formed composite films with the MgOPs well dispersed in the LCP matrix at a MgOP volume fraction (v MgO ) of up to 34%. These films increased the TC up to 2.0 W m −1 K −1 as the v MgO increased, indicating that the LCP matrix increased the TC to 0.66 W m −1 K −1 . This matrix TC value was similar to the λ // value of the LCP (0.63 W m −1 K −1 ), suggesting that effective heat paths formed between the particles. These heat paths are associated with the matrix LCP aligning the director to follow the lines connecting the particle surfaces. This LCP director distribution was promoted by grafting LCP chains on the particle surfaces.

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Section: Grafting Pthe5b3 On Mgopsmentioning

confidence: 99%

Thermal Conductivity Enhancement of Liquid Crystal Polymer–Solid Particle Composites by Grafting a Main-Chain-Type Liquid Crystal Polymer onto Particle Surfaces

Ishikawa

Kawahara

Tomizawa

et al. 2022

ACS Appl. Polym. Mater.

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“…Polymers are broadly classified into thermoplastic and thermosetting polymers, and it is known that the thermal conductivity of thermoplastic polymers increases when they are stretched. − Recently, it has been reported that the thermal conductivity of polyethylene fiber, a thermoplastic polymer, was increased to 104 W/(m·K), which is equivalent to that of metal, by stretching it to the utmost limit. , In contrast, thermosetting polymers that form a three-dimensional network structure, such as epoxy resin, which is an essential material for electronic circuits, cannot be stretched or otherwise oriented like thermoplastic polymers, making it difficult to significantly improve their thermal conductivity. Therefore, to reduce phonon scattering and achieve high thermal conductivity, it is effective to form a highly ordered higher-order structure inside the polymer by self-alignment of the mesogen backbone, ,− and then to design molecules that increase the cross-linking density by selecting a curing agent . Recently, a research study utilized a mesogen epoxy resin film alone, without the addition of a thermally conductive ceramic filler, and achieved a thermal conductivity of 10 W/(m·K) .…”

Section: Introductionmentioning

confidence: 99%

Higher-Order Structural Analysis of a Transparent and Flexible High Thermal Conductive Liquid Crystalline Elastomer Sheet and Its Composite

Takezawa,

Furukawa,

Nachimuthu

et al. 2024

ACS Omega

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Transparency, flexibility, and high thermal conductivity are trade-offs. Specifically, we have investigated a cross-linked acrylic liquid crystal elastomer (LCE) that exhibits both transparency and flexibility while maintaining a high level of thermal conductivity. The transparent monodomain LCE sheet was achieved through a process of stretching an initially opaque polydomain sheet to 80% elongation and subsequently subjecting it to photocuring. The thermal conductivity in the stretching direction (x) of the monodomain LCE sheet was found to be 1.8 times higher than that of the prestretched polydomain sheet, consistent with findings from previous studies. However, in the orthogonal direction (y) to the stretching (x) direction, the thermal conductivity exhibited an even higher value, being 1.7 times greater than in the x-direction, with a value of 3.0 W/(m•K). This unique observation prompted us to conduct further investigation through higher-order structural analysis of these LCE sheets using 2D wide-angle X-ray scattering (WAXS) analysis. In the transparent sheet, the LCE molecules were aligned in the sheet in the stretching x-direction (monodomain structure) for the out-of-plane direction. However, in the inplane x-direction, the molecular plane spacing exhibited random orientation at a period of 0.45 nm. In contrast, within the ydirection of the inner layer, the molecular plane spacing exhibited a uniaxial horizontal orientation at the same period length as in the x-direction. The heat energy entering into the y-direction once spreads to the x-direction, but it was considered that the reason for the higher thermal conductivity to the y-direction would be forming covalent bonds that function as new heat transmission paths, in the direction intersecting to the x-direction during photocuring. Therefore, we concluded that the synergistic effect of the high level of the ordered inner structure and covalent bonding structure due to cross-linking in the y-direction contributes to its higher thermal conductivity compared to that in the x-direction, which exhibits a random in-plane structure. Additionally, we have fabricated an LCE composite sheet filled with 75 vol % of alumina particles using a polydomain-type LCE as the base material. The composite sheet exhibits remarkable thermal conductivity in the thickness direction, measuring at 9.8 W/(m•K), while maintaining a flexibility characterized by an elastic modulus of 70 MPa. This thermal conductivity surpasses that of a nonmesogenic acrylic composite sheet with identical alumina particle filling, which measured at 3.9 W/(m•K), more than twice as much. The presence of the mesogen skeleton has been demonstrated to enhance heat transfer, even within soft composites, by facilitating the formation of an ordered structure.

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“…In [16], it was shown that the addition of TiO 2 significantly changes the properties of the mixture, and a detailed description of this interaction was given depending on the size of the modifier, while in [17], SiO 2 was used to modify the electro-optical properties of polymer-dispersed liquid crystals. Metal oxides are also used to improve thermal and mechanical properties in epoxy composites, including epoxy compounds with mesogenic units [18][19][20]. Additionally, titanium dioxide is known for its photocatalytic activity and protective properties against the degradative effects of weather conditions, especially UV radiation [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Modification of the Dielectric and Thermal Properties of Organic Frameworks Based on Nonterminal Epoxy Liquid Crystal with Silicon Dioxide and Titanium Dioxide

Okrasa,

Włodarska,

Kisiel

et al. 2024

Polymers

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A nonterminal liquid crystal epoxy monomer is used to create an epoxy–amine network with a typical diamine 4,4′diaminodiphenylmethane. The plain matrix is compared to matrices modified with inorganic fillers: TiO2 or SiO2. Conditions of the curing reaction and glass transition temperatures in the cured products are determined through differential scanning calorimetry and broadband dielectric spectroscopy. The curing process is also followed through optical and electrical observations. The dielectric response of all investigated networks reveals a segmental α-process related to structural reorientation (connected to the glass transition). In all products, a similar process associated with molecular motions of polar groups also appears. The matrix modified with TiO2 exhibits two secondary relaxation processes (β and γ). Similar processes were observed in the pure monomer. An advantage of the network with the TiO2 filler is a shorter time or lower temperature required for optimal curing conditions. The physical properties of cured matrices depend on the presence of a nematic phase in the monomer and nonterminal functional groups in the aliphatic chains. In effect, such cured matrices can have more flexibility and internal order than classical resins. Additional modifiers used in this work shift the glass transition above room temperature and influence the fragility index in both cases.

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Filler surface adsorption of mesogenic epoxy for LC Epoxy/MgO composites with high thermal conductivity

Cited by 8 publications

References 23 publications

Thermal Conductivity Enhancement of Liquid Crystal Polymer–Solid Particle Composites by Grafting a Main-Chain-Type Liquid Crystal Polymer onto Particle Surfaces

Thermal Conductivity Enhancement of Liquid Crystal Polymer–Solid Particle Composites by Grafting a Main-Chain-Type Liquid Crystal Polymer onto Particle Surfaces

Higher-Order Structural Analysis of a Transparent and Flexible High Thermal Conductive Liquid Crystalline Elastomer Sheet and Its Composite

Modification of the Dielectric and Thermal Properties of Organic Frameworks Based on Nonterminal Epoxy Liquid Crystal with Silicon Dioxide and Titanium Dioxide

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