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We present a short communication to discuss some of the results of two works by Fujitstuka et al. [M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, A. Watanabe, O. Ito, Chem. Lett. (1997) 1211; M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, O. Ito, K. Yase, J. Photochem. Photobiol. A 133 (2000) 45] in which the photochemical and photophysical properties of a dispersion of fullerene fine particles are discussed. One of the simplest way to growth organic fine particles is the reprecipitation method. In this way microcrystals of fullerene molecules can be obtained with a good control on dimension and size distribution of the final aggregates. The existence and the distribution of fullerene clusters in these liquid solutions is usually attained and characterized by dynamic light scattering technique. In this short communication we want to address a common mistake derived from the widely used reprecipitation method. We show that photoncorrelation measurements from [M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, A. Watanabe, O. Ito, Chem. Lett. (1997) 1211; M. Fujitsuka, H. Kasai, A. Masuhara, S. Okada, H. Oikawa, H. Nakanishi, O. Ito, K. Yase, J. Photochem. Photobiol. A 133 (2000) 45] are faulty due to the presence of a microemulsion between the two solvents used. In ethanol/carbon disulfide mixtures, CS2 droplets dispersed in ethanol mimic in fact the existence of ≈ 300 nm clusters which, actually, do not exist.

Microgel particles composed of Interpenetrated Polymer Network (IPN) of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAAc) dispersed in water have been investigated through dynamic light scattering. The study of the temperature, concentration and pH dependence of the relaxation time has highlighted the existence of a thermoreversible transition corresponding to the swollen-shrunken volume phase transition. The presence of PAAc introduces an additional pH-sensitivity with respect to the temperature-sensitivity due to PNIPAM and leads to interesting differences in the transition process at acid and neutral pH. © 2014 Elsevier B.V. All rights reserved.

Microgels composed of stimuli responsive polymers have attracted worthwhile interest as model colloids for theorethical and experimental studies and for nanotechnological applications. A deep knowledge of their behaviour is fundamental for the design of new materials. Here we report the current understanding of a dual responsive microgel composed of poly(N-isopropylacrylamide) (PNIPAM), a temperature sensitive polymer, and poly(acrylic acid) (PAAc), a pH sensitive polymer, at different temperatures, PAAc contents, concentrations, solvents and pH. The combination of multiple techniques as Dynamic Light Scattering (DLS), Raman spectroscopy, Small Angle Neutron Scattering (SANS), rheology and electrophoretic measurements allow to investigate the hydrodynamic radius behaviour across the typical Volume Phase Transition (VPT), the involved molecular mechanism and the internal particle structure together with the viscoelastic properties and the role of ionic charge in the aggregation phenomena.

The phase behaviour of soft colloids has attracted great attention due to the large variety of new phenomenologies emerging from their ability to pack at very high volume fractions. Here we report rheological measurements on interpenetrated polymer network microgels composed of poly(N-isopropylacrylamide) (PNIPAM) and polyacrylic acid (PAAc) at fixed PAAc content as a function of weight concentration. We found three different rheological regimes characteristic of three different states: a Newtonian shear-thinning fluid, an attractive glass characterized by a yield stress, and a jamming state. We discuss the possible molecular mechanisms driving the formation of these states.

Clay-polymer compounds have recently attracted increasing attention due to their intriguing physical properties in colloidal science and their rheological non-trivial behaviour in technological applications. Aqueous solutions of Laponite clay spontaneously age from a liquid up to an arrested state of different nature (gel or glass) depending on the colloidal volume fraction and ionic strength. We have investigated, through dynamic light scattering, how the aging dynamics of Laponite dispersions at fixed clay concentration (Cw ¼ 2.0%) is modified by the addition of various amounts of poly(ethylene oxide) (PEO) (CPEO ¼ (0.05 O 0.50) %) at two different molecular weights (Mw ¼ 100 kg mol1 and Mw ¼ 200 kg mol1 ). A surprising and intriguing phenomenon has been observed: the existence of a critical polymer concentration C* PEO that discriminates between two different aging dynamics. With respect to pure Laponite systems the aging will be assisted (faster) or hindered (slower) for PEO concentrations respectively lower (CPEO < C* PEO) or higher (CPEO > C* PEO) than the critical concentration. In this way a control on the aging dynamics of PEO-Laponite systems is obtained. A possible explanation based on the balance of competitive mechanisms related to the progressive saturation of the clay surface by polymers is proposed. This study shows how a real control on the aging speed of the PEO-Laponite system is at hand and renders possible a real control of the complex interparticle interaction potential.

A dynamic light scattering (DLS) investigation of the isotopic H/D substitution on water molecules in aqueous Laponite suspensions is reported for two Laponite weight concentrations (C-w = 1.5% and C-w = 3.0%). Increasing the deuterium percentage results in a slowing down of the dynamics for both concentrations, although the aging behavior of the suspensions is not qualitatively modified by the isotopic substitution. A scaling law for the isotopic effect is found. The relaxation times and the stretching parameters collapse on two distinct master curves, indicating that the two previously found dynamical behaviors of colloidal gels and glasses are preserved. These results may facilitate a large variety of experimental techniques and further theoretical investigations about the role of the solvent in determining the interaction potential.