Direct observation of polymer surface mobility via nanoparticle vibrations

Abstract

Measuring polymer surface dynamics remains a formidable challenge of critical importance to applications ranging from pressure-sensitive adhesives to nanopatterning, where interfacial mobility is key to performance. Here, we introduce a methodology of Brillouin light spectroscopy to reveal polymer surface mobility via nanoparticle vibrations. By measuring the temperature-dependent vibrational modes of polystyrene nanoparticles, we identify the glass-transition temperature and calculate the elastic modulus of individual nanoparticles as a function of particle size and chemistry. Evidence of surface mobility is inferred from the first observation of a softening temperature, where the temperature dependence of the fundamental vibrational frequency of the nanoparticles reverses slope below the glass-transition temperature. Beyond the fundamental vibrational modes given by the shape and elasticity of the nanoparticles, another mode, termed the interaction-induced mode, was found to be related to the active particle–particle adhesion and dependent on the thermal behavior of nanoparticles.

Revealing structural evolution occurring from photo-initiated polymer network formation

“…The growth of these heterogeneities is diminished already after 0.5 s. The minimum correlation length within the HT resin is also unaffected by the polymerization time, yet highly reduced to R corr;HT ¼ (28.6 ± 1.2) nm. The correlation length difference is ≈ 20 nm and as the differences in growth kinetic between LT and HT are related to a different molecular cooperative segmental mobility in the two systems, as also seen from the different T g (LT = −17.3°C and HT = 40.5°C) 27 . Fig.…”

Glass Transition of Disentangled and Entangled Polymer Melts: Single-Chain-Nanoparticles Approach

“…In addition, BLS identifies a second so-called softening temperature, T s (< T g ), which is related to the onset of particle surface mobility below T g . 51 , 52 Because the BLS intensity strongly decreases with the NP diameter, the fundamental quadrupolar vibration mode, (1,2), cannot be resolved for NP diameter below about 100 nm. In the presence of NP adhesion, however, a new interaction-induced branch (1,1) representative of few NPs vibration is discernible in the BLS spectrum at frequencies lower than the (1,2) mode.…”

“…In this context, we should also note that the presence of T s indicates an increased mobility of the free SCNP surface, activating surface contacts at T < T g . 51 This surface mobility might lead to the slightly lower apparent T g of the SCNPs (large surface/volume ratio).…”

“…Note that because of different mechanisms and heating rates, the T g estimated by BLS can be about 7–10 K lower than the corresponding DSC value ( Figure 3 a). 49 − 51 …”

Temporal superoscillations of subterahertz coherent acoustic phonons

“…Such acoustic nanowaves can be used to probe the structural and mechanical properties of matter with subnanometer (sub-nm) axial resolution and submicrometer (subμm) transverse resolution [2]. Examples of the applications include studies of various nano-objects [3,4], interfaces [5], defects in solids [6], soft condensed matter [7], liquids [8], and biological matter (single cells) [9] (for a review see also [10]). Acoustic nanowaves have also been used for ultrafast control of photonic [11], electronic [12], and spintronic [13] devices.…”