Ian Ratcliffe

Control of the properties of xanthan/glucomannan mixed gels by varying xanthan fine structure.

The interaction of native xanthan gum, deacetylated xanthan gum and depyruvated xanthan gum with konjac glucomannan has been studied using DSC and controlled stress rheometry. In the absence of electrolyte the DSC cooling curves for native xanthan and deacetylated xanthan showed a single peak and there was a corresponding sharp increase in the storage modulus indicating gel formation. It is apparent that on cooling, association of the konjac glucomannan with the native xanthan molecules is triggered by the xanthan coil-helix transition. In the presence of electrolyte, there were two DSC peaks observed. The higher temperature DSC peak was attributed to the xanthan coil-helix transition while the lower temperature DSC peak was attributed to konjac glucomannan-xanthan association as noted by an increase in the storage modulus. The gels formed were much weaker than those in the absence of electrolyte. The DSC cooling curves for depyruvated xanthan in the absence of electrolyte showed two peaks. The higher temperature peak was attributed to the coil-helix transition while the lower temperature peak corresponded to gelation as noted by an increase in the storage modulus. The gels were very much weaker than for native xanthan gum and deacetylated xanthan gum.

Synthesis, characterization and self-assembly of biosurfactants based on hydrophobically modified inulins.

Biosurfactants have been synthesized using a low energy, environmentally friendly process by the derivatization of inulin with octenyl (OSA) and dodecenyl (DDSA) succinic anhydrides in aqueous solution. The inulin and its derivatives have been characterized using gel permeation chromatography/multi angle light scattering (GPC/MALLS), high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), Fourier transform infrared spectroscopy (FTIR), and NMR, and the reaction efficiency was found to be between 59 and 95%. The efficiency was generally higher for OSA derivatives compared to DDSA derivatives. The hydrophobic derivatives were found to aggregate in solution and the critical aggregation concentration (CAC) was determined using dye solubilization, surface tension, dynamic light scattering (DLS), and conductivity. There was reasonable agreement in the CAC values obtained by the different techniques except for conductivity. It was found that the CAC decreased with increasing alkenyl chain length and degree of modification, and the values were significantly lower for the DDSA derivatives compared to the OSA derivatives. GPC elution profiles for the DDSA-inulin using 12 mol % reagent confirmed the presence of aggregates with a molecular mass of ∼2.5 × 10(6) g/mol and a radius of gyration of ∼25 nm corresponding to ∼550 inulin molecules. DLS study was undertaken to determine the hydrodynamic radius, and values obtained for the DDSA (12%) derivative were 30 nm in both water and 0.1 M sodium nitrate, while for the OSA (12%) derivative values of 13 and 7 nm were obtained. The derivatives have potential application in the stabilization of particulate dispersions and emulsions and also in the encapsulation and delivery of drugs.

Small strain deformation measurements of konjac glucomannan solutions and the influence of borate cross-linking.

The dynamic rheology of aqueous solutions of konjac glucomannan has been evaluated over a range of concentrations up to 2.35%, and the effect of borate cross-linking of such solutions evaluated in the range 0.02-40 mM borate. In preliminary work, conventional parallel plate geometries were employed and in situ cross-linking was investigated. For borate cross-linked samples a superior method, however, was found to be measurement of pre-formed cores of cross-linked polymer into which a four-bladed vane geometry was introduced. In order to compare with other associating polymer systems, rheological data were analysed by defining plateau moduli, corresponding relaxation times and zero shear viscosities and the scaling behaviour of these parameters with polymer and cross-linker concentrations was established. Maxwell fits and time-concentration superposition procedures were investigated. The rheological properties of the cross-linked polymer were shown to be the result of both increased network connectivity and retarded network dynamics.

Self-Assembly and Emulsification Properties of Hydrophobically Modified Inulin

A series of alkenylated inulin samples were synthesized in aqueous solution using alkenyl succinic anhydrides with varying alkenyl chain lengths (C8-C18). The inulin derivatives (ASA-inulins) were characterized using NMR and FTIR and their degree of substitution determined. The solution properties of ASA-inulins were investigated using dye solubilization, surface tension, and dynamic light scattering, and all three techniques confirmed that the molecules aggregated in solution above a critical concentration (critical aggregation concentration, CAC). The value of the CAC was found to be reasonably consistent between the different techniques and was shown to decrease with increasing alkenyl chain length, from 0.08% for the octenyl succinylated sample to 0.005% for the octadecenyl succinylated sample. The hydrodynamic diameter of ASA-inulins above the CAC was determined from dynamic light scattering studies and was shown to increase with alkenyl chain length, from 4 nm for the octenyl derivative to 55 nm for the hexadecenyl derivative. All ASA-inulins were shown to be able to produce oil-in-water emulsions with a droplet size similar to that of emulsions prepared using Tween 20 on storing for 21 days. The fact that the derivatives are able to form micellarlike aggregates and stabilize emulsions makes them suitable candidates for the encapsulation and delivery of water-insoluble active compounds, with potential application in food, cosmetic, personal care, and pharmaceutical formulations.

Small deformation measurements of transient gels using vane rheometry

Measurement of a model transient gel system, i.e. pre-gelled borate cross-linked konjac glucomannan (KGM) has been facilitated by the use of a controlled stress rheometer in conjunction with a stainless steel vane geometry. Calibration of the vane was undertaken in both shear flow and oscillation and enabled reproduction of data recorded using traditional cone and plate and couette fixtures. The transient nature of the borate cross-links coupled with the sharp blades of teh vane facilitated ‘healing’ of the gel around the geometry, resulting in minimal disturbance to the gel. Alternative techniques employed to measure these gels include in-situ gelation in a parallel plate geometry. Using this method difficulties in achieving sample homogeneity imposed serious restrictions upon the range of polysaccharide and borate concentrations that could be studied, and long in-situ gelation times were unavoidable. The microstructure of borate cross-linked KGM gels has been investigated by small strain oscillation measurements using the vane and the trends in the network relaxation times with variation in both polysaccharide concentration and borate concentration established.

Estimation of the particle concentration in hydraulic liquid by the in-line automatic particle counter based on the CMOS image sensor

Modern hydraulic systems should be monitored on the regular basis. One of the most effective ways to address this task is utilizing in-line automatic particle counters (APC) built inside of the system. The measurement of particle concentration in hydraulic liquid by APC is crucial because increasing numbers of particles should mean functional problems. Existing automatic particle counters have significant limitation for the precise measurement of relatively low concentration of particle in aerospace systems or they are unable to measure higher concentration in industrial ones. Both issues can be addressed by implementation of the CMOS image sensor instead of single photodiode used in the most of APC. CMOS image sensor helps to overcome the problem of the errors in volume measurement caused by inequality of particle speed inside of tube. Correction is based on the determination of the particle position and parabolic velocity distribution profile. Proposed algorithms are also suitable for reducing the errors related to the particles matches in measurement volume. The results of simulation show that the accuracy increased up to 90 per cent and the resolution improved ten times more compared to the single photodiode sensor.

Synthesis, characterisation and physicochemical properties of hydrophobically modified inulin using long-chain fatty acyl chlorides

A series of inulin derivatives were synthesized in aqueous solution using acyl chlorides with varying alkyl chain length (C10-C16). They were characterised using a number of techniques including MALDI TOF-MS, 1H NMR and FTIR and their degree of substitution determined. The solution properties of the hydrophobically modified inulins were investigated using dye solubilisation and surface tension and it was confirmed that the molecules aggregated in solution above a critical concentration (critical aggregation concentration, CAC). The value of the CAC was found to be reasonably consistent between the different techniques and was shown to decrease with increasing hydrophobe chain length. It was found that the C10, C12 and C14 derivatives formed stable oil-in-water emulsions and the emulsion droplet size decreased with increasing alkyl chain length. The C16 derivative was not able to produce stable oil-in-water emulsions; however, it was able to form stable water-in-oil emulsions. The fact that the derivatives are able to form micellar-like aggregates and stabilise emulsions makes them suitable candidates for the encapsulation and delivery of active compounds with potential application in food, cosmetic, personal care and pharmaceutical formulations.