The mechanical properties of particulate nanocomposites strongly depend upon the particle dispersion, as well as on the closely related properties in thin polymer films covering the particle surface. The length scale of such changes is relevant for the understanding of particle–particle interactions, which ultimately dominate the mechanical response. Using well-defined 44 nm diameter silica nanoparticles dispersed in poly(ethylene glycol), we focus on surface-induced changes in polymer dynamics. Using proton time-domain NMR, we distinguish three polymer phases of different mobility, i.e., a strongly adsorbed, solid-like fraction, a fraction with intermediate relaxation times and a highly mobile fraction. We explore how these fractions change as we vary polymer molecular weight from 300 to 20 000 and particle volume fraction up to 0.3. A multiple-quantum experiment enables a closer analysis of the mobile component which we show consists of two fractions, one resembling the bulk melt-like and another one showing network-like properties. We demonstrate that above a polymer molecular weight-dependent volume fraction, polymers form elastically active links between particles, resulting in the physical gelation observed in such systems. Our results provide a quantitative picture of network formation, which is described by the amount and length of network-like chains as well as heterogeneities in the polymer dynamics. We relate changes in polymer dynamics to particle microstructure obtained from small angle neutron scattering.

Synthesis of a polymer composed of a large discrete number of chemically distinct monomers in an absolutely defined aperiodic sequence remains a challenge in polymer chemistry. The synthesis has largely been limited to oligomers having a limited number of repeating units due to the difficulties associated with the step-by-step addition of individual monomers to achieve high molecular weights. Here we report the copolymers of α-hydroxy acids, poly(phenyllactic-co-lactic acid) (PcL) built via the cross-convergent method from four dyads of monomers as constituent units. Our proposed method allows scalable synthesis of sequence-defined PcL in a minimal number of coupling steps from reagents in stoichiometric amounts. Digital information can be stored in an aperiodic sequence of PcL, which can be fully retrieved as binary code by mass spectrometry sequencing. The information storage density (bit/Da) of PcL is 50% higher than DNA, and the storage capacity of PcL can also be increased by adjusting the molecular weight (~38 kDa).

Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles.