Soft Composite Gels with High Toughness and Low Thermal Resistance through Lengthening Polymer Strands and Controlling Filler

Abstract

Soft gels with high toughness have drawn tremendous attention recently due to their potential applications in flexible electronic fields. The miniaturization and high‐power density of electronic devices require soft gels with both high toughness and low thermal resistance; however, it is difficult to achieve these properties simultaneously. Herein, a simple design strategy is reported for constructing soft (high stretchability of 6.91 and low Young's modulus of 340 kPa), tough (4741.48 J m−2) and thermal conductive (low thermal resistance of 0.14 cm2 K W−1, under 10 psi pressure) polydimethylsiloxane/aluminum composite gel. This is realized by precisely lengthening polymer strands between the chemical cross‐linked points and controlling the aluminum content in the composite gels. The symbiosis of this combination involves: lengthening the polymer strands facilitates its unfolding to increase the softness and intrinsic toughness; the thermally conductive spherical aluminum enables low thermal resistance and increases the intrinsic toughness and stress dissipation. By utilizing this gel as a thermal interface material, effective heat dissipation is demonstrated in electronic devices operating under high‐power conditions over numerous cycles. These results demonstrate the application potential of composite gels in meeting the performance maintenance and heat dissipation, which are needed for modern electronic devices.

Soft, Tough, and Thermally Conductive Elastomer Composites by Constructing a Curled Conformation

“…There is no obvious difference between the C-PDMS/60 wt % BN and E-PDMS/60 wt % BN in the relaxation frequency of the cross-linked networks. 25 Furthermore, the classical theory of rubber elasticity predicts the stress−strain relation of the network composed of Gaussian chains as σ e /G = λ − λ −2 . 28,29 Figure 3d shows the double logarithmic plot of σ e /G versus λ − λ −2 for the C-PDMS/60 wt % BN and C-PMDS/BN, where G is the shear modulus and the relation G = E/3 for incompressible materials was used.…”

“…As shown in Figure a, we used a rotational rheometer to measure the storage modulus ( G ′) and loss modulus ( G ″) of the C-PDMS/60 wt % BN and E-PDMS/60 wt % BN at different frequencies. According to their plateau modulus in the low frequency region, the average molecular weight between cross-links ( M x ) was estimated using eq : G p = ρ R T M x where ρ is the density of the PDMS/60 wt % BN elastomer composites, R is the ideal gas constant, and T is the absolute temperature. According to our design concept, the solvent can promote the disentanglement of the molecular chain.…”

“…As shown in Figure 3a, we used a rotational rheometer to measure the storage modulus (G′) and loss modulus (G″) of the C-PDMS/ 60 wt % BN and E-PDMS/60 wt % BN at different frequencies. According to their plateau modulus in the low frequency region, the average molecular weight between crosslinks (M x ) was estimated using eq 1: 25 (1…”

“…In addition, the relaxation mechanism at a relaxation frequency of 0.001–0.01 rad/s is attributed to the relaxation between BN fillers, and the relaxation mechanism with the maximum relaxation frequency (10–100 rad/s) belongs to the motion of the cross-linked network. There is no obvious difference between the C-PDMS/60 wt % BN and E-PDMS/60 wt % BN in the relaxation frequency of the cross-linked networks …”

Dry-Contact Thermal Interface Material with the Desired Bond Line Thickness and Ultralow Applied Thermal Resistance

“…Now, considerable attention has been paid to the development of high- k materials, and many attempts at highly thermally conductive TIMs have been witnessed in the past two decades. − For example, carbon nanotubes (CNTs) are the ideal TIM precursor due to their one-dimensionally highly thermo-conductive characteristic (≥2000 W/m K) . Various vertically aligned technologies were adopted to successfully fabricate perpendicular CNTs-array TIMs, whose out-of-plane k were reported to be able to exceed 70 W/m K. , Similar results can also be found in vertical graphene TIMs, for example, a mechanical-machining processed graphene monolith was manifested to exhibit an out-of-plane k as high as 143 W/m K, which is on par with some metals and alloys. , In addition to the above high- k carbons, other TIMs include liquid metals, ,, inherently thermally conductive polymers, polymer composites (i.e., thermal grease, gel, and pad), − and phase change materials. − Looking at the previously reported TIMs, the manipulation of the anisotropic k and making it superb in the thickness direction is not a very difficult thing; however, the achievement of a low R eff when these TIMs are applied in a sandwiched heat source-sink structure remains a formidable challenge. Taking one of the most mature and commercial dry-contact TIMs (thermal grease) as an example, its applied thermal resistance in a sandwiched structure is rarely found to be lower than 5 mm 2 K/W, a boundary value that traditional solders can perform .…”