Higher contact angles or amplified wettability observed on surfaces of rough solid materials are typically expressed as a function of a physical dimension (roughness factor). Herein, we present a simple experimental approach that demonstrates that roughness may only magnify the inherent surface chemistry that seems to have direct influence on surface wettability. We investigate gradual change in surface chemistry (hydrophobisation) of rough and smooth glass surfaces, from a very low concentration (10⁻⁷ M) of dichlorodimethylsilane, DCDMS through various intermediate hydrophilic/hydrophobic states to when the surfaces are maximally hydrophobised with DCDMS at 0.1 M. The wettability of the modified glasses was studied by water contact angle measurements using drop shape analysis system (DSA). The data obtained indicate a deviation from Wenzel model, with the functionalized rough glass surfaces showing higher reactivity towards DCDMS when compared to the smooth glass surfaces, indicating that the two surfaces are not chemically identical. Our study reveals that just like transforming a solid material to powder, a well-divided glass (rough) surface may not only exhibit a greater surface area than the smooth counterpart as rightly predicted by the Wenzel model, but seems to be bloated with functional groups (–OH or –CH₃) that can amplify surface interaction when such functional species dominate the solid surface.

Cross-linked cellulose-epichlorohydrin polymers were synthesized by a conventional heating with stirring (C-EP heating) and a parallel process using ultra-sonication (C-EP sonication) in the presence of aqueous ammonia. Structural characterization of modified cellulose was carried out using FTIR/13C solid state NMR spectroscopy and thermal methods (DSC and TGA). Evidence of products with variable textural properties and morphology was supported by nitrogen gas adsorption, solvent swelling, and microscopy (SEM, TEM) results. C-EP sonication possess greater cross-linker content judging by the loss of the cellulose fibril structure which was facilitated by acoustic cavitation effects due to ultra-sonication. Equilibrium sorption studies in aqueous solution with 2-naphthoxy acetic acid (NAA) revealed that C-EP heating had slightly greater sorption capacity than C-EP sonication at alkaline pH. By contrast, C-EP sonication had greater uptake of NAA at acidic pH. Kinetic uptake studies at pH 3 is described by the pseudo-second order model, where the surface sites of C-EP heating became saturated within ca. 75 min; whereas, ca. 350 min occurred for C-EP sonication. This study demonstrates that the yield of sonication assisted cross-linking of cellulose is greater with improved adsorption properties. The study also reveals the utility of sonication assisted synthesis for the valorization and utilization of cellulose modified materials.

The sorptive uptake properties are reported for chitosan and cross-linked chitosan-glutaraldehyde (CG) polymers with single component carboxylic acids (surrogates; Si, i = 1–4). The single component surrogates are treated as model compounds to represent traditional naphthenic acids (NAs) with variable hydrogen deficiency (z) and carbon number (C), as follows: 2-hexyldecanoic acid (z = 0 and C = 16; S1), trans-4-pentylcyclohexanecarboxylic acid (z = −2 and C = 12; S2), dicyclohexylacetic acid (z = −4; C = 14; S3) and 2-ethyl hexanoic acid (z = 0 and C = 8; S4). Cross-linked polymers were synthesized at variable C : G mole ratios (i.e. 1 : 400, 1 : 700, and 1 : 1000) and characterized using FTIR and TGA. The uptake studies were evaluated at pH 6.00 and 9.00 in aqueous solution. Corresponding equilibrium uptake parameters were evaluated by several isotherm models (Sips, Freundlich, and Langmuir). The Freundlich model provided the “best-fit” for S1, S2 and S3. The Sips isotherm model gave the “best-fit” results for S4. The Freundlich sorption affinity constant (K_F; L mg g⁻¹) and the Sips monolayer adsorption capacity (Q_m; mg g⁻¹) for the sorbent systems was estimated. The parameters for each Si vary as the C : G mole ratio increases (K_F, S1: 0.00800–6.65, S2: 1.41–2.45, S3: 1.29–2.93 and Q_m, S4: 28.4–33.5). Differences in the uptake of Si species by the sorbents were attributed to steric effects between Si with ring systems (z < 0) versus linear alkyl fragments (z = 0). Fractionation of equimolar mixtures of Si reveal that the sorbents display unique and variable binding affinity with remarkable molecular selective uptake (given in parentheses; L mg g⁻¹): S1 (4–30) > S2 (4–10) > S3 (3–9). The fractionation efficacy of Si species is attributed to molecular sieving effects due to the tunable micropore sites of the cross-linked polymer, in accordance with the variable cross-linker content of the chitosan framework. Regeneration studies revealed the utility of these materials in cyclic adsorption–desorption processes.

Quaternized (QC) and cross-linked/quaternized (CQC) cellulose hydrogels were prepared by cross-linking native cellulose with epichlorohydrin (ECH), with subsequent grafting of glycidyl trimethyl ammonium chloride (GTMAC). Materials characterization via carbon, hydrogen and nitrogen (CHN) analysis, thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR)/¹³C solid state NMR spectroscopy provided supportive evidence of the hydrogel synthesis. Enhanced thermal stability of the hydrogels was observed relative to native cellulose. Colloidal stability of octanol and water mixtures revealed that QC induces greater stabilization over CQC, as evidenced by the formation of a hexane–water Pickering emulsion system. Equilibrium sorption studies with naphthenates from oil sands process water (OSPW) and 2-naphthoxy acetic acid (NAA) in aqueous solution revealed that CQC possess higher affinity relative to QC with the naphthenates. According to the Langmuir isotherm model, the sorption capacity of CQC for OSPW naphthenates was 33.0 mg/g and NAA was 69.5 mg/g. CQC displays similar affinity for the various OSPW naphthenate component species in aqueous solution. Kinetic uptake of NAA at variable temperature, pH and adsorbent dosage showed that increased temperature favoured the uptake process at 303 K, where Q_m = 76.7 mg/g. Solution conditions at pH 3 or 9 had a minor effect on the sorption process, while equilibrium was achieved in a shorter time at lower dosage (ca. three-fold lower) of hydrogel (100 mg vs. 30 mg). The estimated activation parameters are based on temperature dependent rate constants, k₁, which reveal contributions from enthalpy-driven electrostatic interactions. The kinetic results indicate an ion-based associative sorption mechanism. This study contributes to a greater understanding of the adsorption and physicochemical properties of cellulose-based hydrogels.