Methods for probing the long-range dynamic of confined polymers in nanoparticles using small-angle neutron scattering

Abstract

Motivated by the recent advances in new technologies, a lot of effort has been dedicated to developing methods for quantifying the dynamic of nanoconfined polymers. Particularly, polymers confined in nanoparticles are an important system for several environment-friendly applications such as waterborne coatings and nanoblends. In this work, we discuss two methods to probe the large scale dynamic of nanoconfined polymers in nanoparticles in two situations: (i) nanoblends and (ii) the close-packed structure. In the methods we apply stress at the nanoscopic level around the polystyrene particles and we probe their deformation in real time using small-angle neutron scattering. These methods give new possibilities to probe, in a nonintrusive manner, the dynamic of confined polymers in nanoparticles, which could ultimately bring conclusive insight to this field. Résumé :Motivés par les développements récents dans les nouvelles technologies, beaucoup d'efforts ont été déployés dans le but de mettre au point des méthodes permettant de quantifier la dynamique des polymères nanoconfinés. En particulier, les polymères confinés dans des nanoparticules sont des systèmes importants pour plusieurs applications respectueuses de l'environnement, tels les enduits et les mélanges aqueux. Dans ce travail, on discute de deux méthodes d'étudier la dynamique à grande échelle des polymères nanoconfinés dans des nanoparticules, dans deux situations: (i) les nanomélan-ges et (ii) la structure à grande compacité. Dans ces méthodes, on applique un stress au niveau nanoscopique autour des particules de polystyrène et on étudie leur déformation en temps réel en faisant appel à la diffusion des neutrons à angles faibles. Ces méthodes fournissent de nouvelles possibilités pour étudier, d'une façon non intrusive, la dynamique des polymères confinés dans des nanoparticules et elles pourraient éventuellement permettre d'obtenir un éclairage conclusif pour comprendre ce champ.

Heat Capacity of Confined Polystyrene in Close-Packed Particles

“…In Figure , our results are presented with green squares and are compared to the Torkelson results and the Nawaz et al results. The α-relaxation of confined polystyrene in particles as small as 69 nm did not show any deviation from bulk behavior when measured in the temperature range between 100 and 80 °C, where C p deviates from bulk.…”

“…Figure 8 shows the shift factor between 100 and 80 °C vs inverse temperature and compared to dynamics bulk and confined particles using the neutron scattering technique. 40 In Figure 8, our results are presented with green squares and are compared to the Torkelson results 41 and the Nawaz et al 40 results. The α-relaxation of confined polystyrene in particles as small as 69 nm did not show any deviation from bulk behavior when measured in the temperature range between 100 and 80 °C, where C p deviates from bulk.…”

“…The a T is estimated from the decays of Figure7busing the 100 °C as the reference temperature. The a T for the nanoparticles (69 nm) is compared to the shift factor, estimated from the void closure experiment for polystyrene particles of different sizes using small-angle neutron scattering (○) and to that of the bulk polystyrene ( □ ) made from the same particles using the creep compliance experiments (Rharbi et al29 ) and to that of a T of bulk of other polystyrene () reported from Torkelson's results 41. The temperature is normalized to the bulk T g .…”

The Dynamic of Confined Polystyrene in Nanoparticles in the Glassy Regime: The Close Packed Morphology

“…When PS particles were dispersed in nanoblends, they were also found to adopt different mechanical properties than bulk particularly for particles smaller than 45 nm. , However, the effect of confinement in nanoparticles on the dynamic of polymers still remains an open question. We have shown in previous work that it is possible to directly probe the relaxation time of polystyrene in nanoparticles using the kinetic of void closure between close-packed particles. , In these experiments we found that when water is evaporated from the particle suspension in the glassy regime, the particles remain spherical and form close-packed structures separated by interstices (voids). , The presence of free surface area within these interstices (Scheme ) is what gives the confined particularity to the polymer. The air/polystyrene surface tension γ P/a (γ P/a = 0.03 N/m 2 ) in the voids generates negative Laplace pressure P lap = γ P/a S void / V void (where S void and V void are the surface and volume of the voids) which close the voids and deform the particles. ,, We demonstrated that particle deformation can be used to quantify the relaxation time of the confined polymer in particles. , …”

“…These particles are synthesized via emulsion polymerization in the aqueous phase with controlled sizes larger than 20 nm. They are used in several applications such as the water-born coating industry. − A few groups have investigated the dynamic and the glass transition of polymers confined in particles. For example Sasaki et al, using dynamical scanning calorimetry (DSC) on aqueous suspensions of polystyrene particles, observed a reduction of the heat capacity (Δ C p ) when decreasing the particle size and did not detect any shift of T g .…”