30 research outputs found
Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study
The behavior of water molecules surrounding a protein can have an important bearing on its structure and function. Consequently, a great deal of attention has been focused on changes in the relaxation dynamics of water when it is located at the protein surface. Here we use the ultrafast optical Kerr effect to study the H-bond structure and dynamics of aqueous solutions of proteins. Measurements are made for three proteins as a function of concentration. We find that the water dynamics in the first solvation layer of the proteins are slowed by up to a factor of 8 in comparison to those in bulk water. The most marked slowdown was observed for the most hydrophilic protein studied, bovine serum albumin, whereas the most hydrophobic protein, trypsin, had a slightly smaller effect. The terahertz Raman spectra of these protein solutions resemble those of pure water up to 5 wt % of protein, above which a new feature appears at 80 cm–1, which is assigned to a bending of the protein amide chain
Graphene -- Based Nanocomposites as Highly Efficient Thermal Interface Materials
We found that an optimized mixture of graphene and multilayer graphene -
produced by the high-yield inexpensive liquid-phase-exfoliation technique - can
lead to an extremely strong enhancement of the cross-plane thermal conductivity
K of the composite. The "laser flash" measurements revealed a record-high
enhancement of K by 2300 % in the graphene-based polymer at the filler loading
fraction f =10 vol. %. It was determined that a relatively high concentration
of single-layer and bilayer graphene flakes (~10-15%) present simultaneously
with thicker multilayers of large lateral size (~ 1 micrometer) were essential
for the observed unusual K enhancement. The thermal conductivity of a
commercial thermal grease was increased from an initial value of ~5.8 W/mK to
K=14 W/mK at the small loading f=2%, which preserved all mechanical properties
of the hybrid. Our modeling results suggest that graphene - multilayer graphene
nanocomposite used as the thermal interface material outperforms those with
carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and
lower Kapitza resistance at the graphene - matrix interface.Comment: 4 figure
Application of Hybrid Fillers for Improving the Through-Plane Heat Transport in Graphite Nanoplatelet-Based Thermal Interface Layers
The in-plane alignment of graphite nanoplatelets (GNPs) in thin thermal interface material (TIM) layers suppresses the though-plane heat transport thus limiting the performance of GNPs in the geometry normally required for thermal management applications. Here we report a disruption of the GNP in-plane alignment by addition of spherical microparticles. The degree of GNP alignment was monitored by measurement of the anisotropy of electrical conductivity which is extremely sensitive to the orientation of high aspect ratio filler particles. Scanning Electron Microscopy images of TIM layer cross-sections confirmed the suppression of the in-plane alignment. The hybrid filler formulations reported herein resulted in a synergistic enhancement of the through-plane thermal conductivity of GNP/Al(2)O(3) and GNP/Al filled TIM layers confirming that the control of GNP alignment is an important parameter in the development of highly efficient GNP and graphene-based TIMs
Effects of Functionalization on Thermal Properties of Single-Wall and Multi-Wall Carbon Nanotube-Polymer Nanocomposites
Carboxylic functionalization (-COOH groups) of carbon nanotubes is known to
improve their dispersion properties and increase the electrical conductivity of
carbon-nanotube - polymer nanocomposites. We have studied experimentally the
effects of this type of functionalization on the thermal conductivity of the
nanocomposites. It was found that while even small quantities of carbon
nanotubes (~1 wt%) can increase the electrical conductivity, a larger loading
fraction (~3 wt%) is required to enhance the thermal conductivity of
nanocomposites. Functionalized multi-wall carbon nanotubes performed the best
as filler material leading to a simultaneous improvement of the electrical and
thermal properties of the composites. Functionalization of the single-wall
carbon nanotubes reduced the thermal conductivity enhancement. The observed
trends were explained by the fact that while surface functionalization
increases the coupling between carbon nanotube and polymer matrix it also leads
to formation of defects, which impede the acoustic phonon transport in the
single wall carbon nanotubes. The obtained results are important for
applications of carbon nanotubes and graphene flakes as fillers for improving
thermal, electrical and mechanical properties of composites.Comment: 25 pages; 6 figure