Elastic and dynamic heterogeneity in aging alginate gels

Anomalous aging in soft glassy materials has generated a great deal of interest because of some intriguing features of the underlying relaxation process, including the emergence of “ultra-long-range” dynamical correlations. An intriguing possibility is that such a huge correlation length is reflected in detectable ensemble fluctuations of the macroscopic material properties. We tackle this issue by performing replicated mechanical and dynamic light scattering (DLS) experiments on alginate gels, which recently emerged as a good model-system of anomalous aging. Here we show that some of the monitored quantities display wide variability, including large fluctuations in the stress relaxation and the occasional presence of two-step decay in the DLS decorrelation functions. By quantifying elastic fluctuation through the standard deviation of the elastic modulus and dynamic heterogeneities through the dynamic susceptibility, we find that both quantities do increase with the gel age over a comparable range. Our results suggest that large elastic fluctuations are closely related to ultra-long-range dynamical correlation, and therefore may be a general feature of anomalous aging in gels

Investigation on the thermal gelation of Chitosan/\u3b2-Glycerophosphate solutions

This work deals with the effect of temperature on the thermal-gelation process of water solutions containing chitosan \u3b2-glycerolphosphate disodium salt hydrate. In particular, the attention is focused on the role played by temperature on the gel final properties, a very important aspect in the frame of drug delivery systems. The study was performed by combining rheology and low field nuclear magnetic resonance, two approaches that revealed to be highly synergic as they can detect different aspects of the developing polymeric network. This study indicates that 30 \ub0C represent a sort of threshold for both the gelation kinetics and the gel final properties. Indeed, above this temperature, gelation kinetics was rapid and yielded to a strong gel. On the contrary, a slow kinetics and a final weak gel occurred below 30 \ub0C. Finally, rheology and low field NMR allowed, independently, evaluating the time evolution of the network mesh size upon gelation

Anomalous Aging and Stress Relaxation in Macromolecular Physical Gels: The Case of Strontium Alginate

We investigate macromolecular physical gels (strontium alginates) in a wide range of aging times and length scales by combining linear stress relaxation and dynamic light scattering (DLS) experiments. Stress relaxation shows an early logarithmic decay followed by a stretched exponential behavior, leading to define two characteristic times, which increase as distinct power laws of gel age. The DLS clearly displays anomalous microscopic dynamics, with compressed exponential decay of autocorrelation functions and ballistic wavelength dependence of the decay time. Thus, our results demonstrate that stretched stress relaxation can coexist with compressed intensity autocorrelation functions. In addition, comparison between rheology and DLS allows for the identification of two characteristic lengths that we interpret as the typical size of collapsing pores in the gel and of avalanche-like rearrangements. We discuss this scenario in terms of some recently proposed ideas on anomalous aging, such as ultralong-ranged dynamical correlations in closely athermal systems

On the acid-responsive release of benzotriazole from engineered mesoporous silica nanoparticles for corrosion protection of metal surfaces

Corrosion inhibitors are largely exploited for the development of highly performing polymeric active coatings. One of the major drawbacks, however, relies in their UV sensitivity, which may compromise their ability to effectively prevent corrosion processes. This issue is particularly relevant in the field of cultural heritage preservation, in which polymeric active coating which are able to ensure a reliable and long-lasting protection against corrosion are highly needed. Besides proving that UV-induced photodegradation impressively lowers the corrosion inhibition ability of benzotriazole (BTA), in the present work we show that this phenomenon can be largely prevented by exploiting inorganic nanocarriers. More specifically, BTA molecules loaded into functionalized mesoporous silica nanoparticles are preserved from photodegradation and released in the host coating only in the presence of acid-related external stimuli. Accelerated corrosion tests carried out on a commercial acrylic-based coating containing engineered mesoporous silica nanoparticles loaded with BTA demonstrated that the developed system possesses an excellent anticorrosion ability