Roles of kink on the thermal transport in single polyethylene chains

Abstract

The trans-gauche state transformation commonly exists in polymers. However, the fundamental understanding of the roles of kink (gauche state) on the thermal energy transport in polymer chains is rather limited. From atomic simulations, we show that kinks greatly scatter phonons in single polyethylene chains, and even a single kink can reflect more than half of the phonons. Further studies show that kinks not only add extra thermal resistance to the chain but also break the whole chain into small segments and each with reduced thermal conductivity. A simple series thermal resistance model is proposed to estimate the effective thermal conductivity of single polymer chains with multiple kinks.

The Role of Polyethylene Wax on the Thermal Conductivity of Transparent Ultradrawn Polyethylene Films

“…By combining eqs 1 and 2 , eq 3 describes both the dependence of the thermal conductivity as a function of Mn and the draw ratio: In the case of a specific draw ratio, the thermal conductivity is described roughly by Mn following the equation below, which is consistent with that in a perfect stretched PE chain. 13 The values of B and γ are approximately 0.206 ± 0.13 and 0.426 ± 0.052 by fitting the data in Figure 4 A and B.…”

“…As mentioned earlier, κ 1 has been described in computer simulations as an exponential function of chain length ( L ). 13 , 14 However, the thermal transport is different in a single PE chain than PE films, 20 as PE chains are difficult to be extended completely in polymer films without entanglements and kinks. 13 Therefore, in our model, κ 1 is described by an exponential function of Mn instead of chain length.…”

“… 13 , 14 However, the thermal transport is different in a single PE chain than PE films, 20 as PE chains are difficult to be extended completely in polymer films without entanglements and kinks. 13 Therefore, in our model, κ 1 is described by an exponential function of Mn instead of chain length. Here, B is a constant and its unit is W/(g/mol) γ m –1 K –1 .…”

“…γ indicates the competition between diffusive and ballistic phonon transport, where diffusive and ballistic phonon transport leads to γ = 0 and 1, respectively. 13 …”

“…Recently, we reported on highly transparent, ultradrawn high-density polyethylene and ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposite films containing graphene and 2-(2 H -benzotriazol-2-yl)-4,6-di- tert -pentylphenol (BZT) as additives 16 , 17 with high thermal conductivity (∼75 W m –1 K –1 ). 13 We now report on the use of polyethylene wax (PE wax ) as an additive to obtain highly transparent, thermally conductive UHMWPE films. Upon the addition of PE wax , the thermal conductivity of the polymer films increases with the highest conductivity being 47 (W m –1 K –1 ), and it decreases again at higher concentrations.…”