Textural Characteristics of Resorcinol—Formaldehyde Resin and Temperature Behavior of Bound Water Affected by Co-Adsorbed Trifluoroacetic Acid or Pyridine in Weakly Polar Organic Media

Resorcinol–formaldehyde resin (RFR) was synthesized as a porous material characterized by specific surface area of 140 m 2 /g and pore volume of 0.59 cm 3 /g with major proportions of broad mesopores and macropores. The interfacial behavior of water at low (h = 0.05 g of water/gram of dry RFR) and high (h = 2 g/g) hydration degrees depends on temperature and pore size filled by unfrozen water because its freezing-point depression increases in narrower pores. When water is mixed with co-adsorbates, the effects of such co-adsorbates as non-polar, weakly polar and polar organics depend on the amounts and the pore sizes. Even at a low hydration degree (h = 0.05 g/g), a portion of water can be displaced from pores by organic co-adsorbates because water has a relatively weak interaction with the RFR surface

A role of free silanol groups of nanosilica surface in interaction with poly(vinyl pyrrolidone)

In this work, a role of the number of free silanol groups at a nanosilica surface (specific surface area SBET = 250 m2/g, initial amount of silanols αОН = 0.60-0.62 mmol/g) was analyzed in interaction with poly(vinyl pyrrolidone) (PVP) vs. the degree (QTMS) of silica hydrophobization by hexamethyldisilazane at 100 oC. The value of QTMS was 0.07, 0.42, 0.67, 0.81, 0.82, and 1.0. Adsorption of PVP onto a nanosilica surface was carried out from a water and water-ethanol (1:1) solutions of the polymer. It was shown that free silanol groups play a crucial role in the adsorption of poly(vinyl pyrrolidone). The value of the maximal adsorption (monolayer capacity) on completely hydrophobic nanosilica surface is approximately by 6.5 times lower than that for unmodified nanosilic

Driving forces of conformational changes in single-layer graphene oxide

The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance