Carmel Jolicoeur

A high-precision digital readout flow densimeter for liquids

A precision densimeter for liquids, based on the oscillating-tube principle, has been designed. The apparatus allows relative density measurements to be carried out routinely with ppm precision, on 5–7 cm3 of solution, in a total time ranging between 5 to 10 min. The results of various tests reported here show the densimeter to be useful for investigation in aqueous as well as nonaqueous media; it is particularly well adapted to accurate measurements of small density increments, as required in excess-volume studies. Since the instrument operates in the flow regime, it is also adaptable to on-line monitoring of density in continuous processes.

Chemical admixture-cement interactions: Phenomenology and physico-chemical concepts

Abstract Chemical admixtures are often used to alter the course of cement hydration reactions and the properties of fresh or hardened concrete. The admixtures, in most cases organic compounds, can perform such functions through various types of physico-chemical interactions with the hydrating cement phases. To understand the consequences of admixture-cement interactions, and to optimize the functional properties of admixtures, appropriate descriptions of their mode of action must be developed. An overview of the latter is attempted here, drawing mainly from: (1) the chemistry and phenomenology of cement hydration; (2) a review of the various types of molecular processes in which admixture molecules can be involved at the solid-solution interface; (3) selected experimental data on the influence of water reducers and superplasticizers which illustrate some basic features of admixture-cement interactions.

Solvation of amino acid residues in water and urea-water mixtures: Volumes and heat capacities of 20 amino acids in water and in 8 molar urea at 25°C

The limiting partial molar volumes Vo and heat capacities Cpo of 20 amino acids have been determined in water and in 8 molar urea at 25.0°C using flow calorimetry and flow densimetry. The side chain contributions to Vo and Cpo were obtained as the difference between the properties of the various amino acids and those of glycine, both in water and in 8M urea. The solvent accessible surface area of the amino acid residues were obtained using a method developed by Hermann, and the total surface areas were separated into their hydrophobic AHb and hydrophilic components. In water, Cpo values for the various residues Cpo(R) were found well correlated with AHb, though much less so in the urea solution. Hence, Cpo(R) values, in water yield a good estimate of side chain hydrophobicity, but the (water→urea) transfer heat capacities appear strongly affected by specific solvation effects in the urea solution.

Phosphate adsorption in flocculation processes of aluminium sulphate and poly-aluminium-silicate-sulphate

Abstract The adsorption of mono-phosphate ions from aqueous solutions by flocs formed upon hydrolysis of alum (Al2(SO4)3) and a basic alum (poly-aluminium-silicate-sulphate [PASS]) was investigated as a function of pH (5–7), phosphate concentration (0–0.53 m m or 0–50 ppm) and coagulant concentration. The PO4 adsorption processes were examined—first, on pre-formed flocs of alum or PASS and, second, upon in-situ floc formation, e.g. hydrolysis and flocculation in the presence of PO4 ions. The PO4 adsorption data, together with zeta-potential results, show that the PO4-floc interactions on pre-formed flocs involve mainly specific interactions accompanied by H+ or OH− exchange; with in-situ hydrolysis, complexation and charge neutralization effects play a significant part. On pre-formed flocs, PO4 binding does not distinguish between alum and PASS. Upon in-situ hydrolysis and coagulation, PASS floc binds less PO4 than alum floc, due to the higher cationic charge of the latter; however, PASS yields a floc which is larger and more resistant to shear stress than the floc obtained with alum, particularly at low pH.

A comprehensive thermodynamic investigation of water-ethylene glycol mixtures at 5, 25, and 45°C

A detailed thermodynamic study of water (W)-ethylene glycol (EG) mixtures has been carried out as function of temperature (5, 25 and 45°C) and over the entire composition range. The data comprise heats of mixing, densities, heat capacities and compression coefficients. Using excess free energy data from earlier work, molar excess functions were calculated for free energies GE, enthalpies HE and entropies TSE, volumes VE, isobaric and isochoric heat capacities CPE, CVE, adiabatic and isothermal compression KE, KTE and thermal expansion EE, as well as the temperature derivatives of K, C and E functions. The corresponding partial molar quantities were also calculated except for G, H and S and are reported for both EG and W. Also calculated were cohesive energy density, internal pressure and Kirkwood-Buff integrals. The data reported here for EG-W mixtures are compared with similar data for other mixtures as available in order to gain insight into: 1) the relative discriminating ability of various thermodynamic coefficients towards weak cooperative intermolecular interactions in liquids; 2) the quantitative similarities and differences between liquid water and ethylene glycol; 3) the intermolecular phenomena which dominate the properties of EG-W mixtures of varying composition; 4) the usefulness of a qualtitative description of liquid water proposed by Lumry et al. which involves hydrogen-bonding interactions, hydrogen-bonding connectivity and small cooperative fluctuation units.

Steady state and composition scanning differential flow microcalorimeters

Abstract Two different flow microcalorimeters have been constructed. One is of the adiabatic type and can be used to measure ΔTmixing for liquid phase reactions. The other can be operated under either adiabatic or isothermal conditions and serves for either gas or liquid phase investigations. These instruments have similar sensitivities, their thermal detection limit being ≈ 10−5 °C. Enthalpies of reaction involving temperature changes greater than 0.001 °C can be measured with an accuracy of 1 per cent or better; in the isothermal operational mode the heat flux sensitivity is ≈ 0.5 μW. The electrical calibration of the instruments has been checked against the enthalpy of neutralization of 0.005 M HCl with 0.0055 M NaOH in carbonate free water. To estimate the efficiency of mixing in the flow cell, the enthalpy of twofold dilution of aqueous urea solutions has been measured at 0.1 mol kg−1 and higher initial molalities. Both instruments reach steady steates within 1 min. This feature allows the flow rates of the mixing fluids to be varied continuously. Thus curves of enthalpy of mixing against volume fraction can be obtained directly in about 1 h. Some composition-scanning curves are reported for the aqueous systems: NaCl (2 mol kg−1) + KCl (2 mol kg−1) and HCl (0.02 M) + NaOH (0.02 M). Investigation of the latter system at various times of scanning shows that the scanning period can be reduced to 5 to 10 min without severe losses in the thermochemical information. With such characteristics, these instruments can be applied to a wide variety of analytical and thermodynamic problems.

The adsorption behavior of PNS superplasticizer and its relation to fluidity of cement paste

The adsorption behavior of a polynaphthalenesulfonate (PNS) superplasticizer and its relation to the fluidity of cement paste has been investigated for six cements at a given dosage of PNS superplasticizer. The results show that incompatible cements have a higher adsorption capacity of PNS superplasticizer because of a lack of soluble alkali sulfates. There is an inverse relationship between the amount of PNS adsorbed and the mini-slump area value of the cement pastes at 30 min, that is, the higher the amount of PNS adsorbed, the lower the initial slump value, and the higher the slump loss. The addition of some Na2SO4 contributes to increase the slump area by reducing the amount of PNS adsorbed. Moreover, it has been found that additional calcium sulfate does not prevent the adsorption of PNS on cement particles as sodium sulfate does in cement pastes having W/C=0.35. The contribution of alkali sulfate on dispersing mechanism of PNS superplasticized cement pastes is explained in relation with initial slump and its loss.

Geometric relaxation in water. Its role in hydrophobic hydration

The thermodynamic quantities ΔG°, ΔH°, ΔS° and ΔC°p associated with the solvation of argon in water and aqueous mixtures are reinterpreted on the basis of two contributions. The first is related to the hydrogen-bonding connectivity of water and is assumed to be approximately represented by corresponding thermodynamic quantities in solvents such as hydrazine and ethylene glycol; following a proposal by Lumry and Frank [R. Lumry and H. S. Frank, Proc. 6th Int. Biophys. Congr.(1978), vol. 7, p. 554; R. Lumry, in Bioenergetics and Thermodynamics; Model Systems, ed. Y. Braibanti (Reidel, Dordrecht, 1980), p. 405] this contribution determines the free energy of hydrophobic hydration and is dominated by a positive enthalpy. The second contribution, which is responsible for marked enthalpy–entropy compensation and large heat-capacity effects in argon hydration, is assigned to the characteristic fluctuation behaviour of liquid water. This assignment is substantiated by comparisons of the bulk properties of water and various other liquids, and a model is suggested to rationalize the uncommon thermodynamic properties of water, aqueous mixtures and solutions of hydrophobic solutes. The phenomenological representation proposed is an overlay of a randomly connected H-bond network and a local fluctuation process defined in terms of a minimum cooperative unit. This process, labelled “geometric relaxation”, is pictured as a cooperative H-bond rearrangement involving a water molecule coordinated by four neighbours. The limiting microstates of the cooperative units are “short-bond” forms (with short, stiff, near-linear bonds) and “long-bond” forms (with long, weak, bent hydrogen bonds). The first is dominated by the low enthalpy of short hydrogen bonds and the second by the high entropy resulting from motions of the water molecules on flexible hydrogen bonds into the free volume not available to the “short-bond” form.

Mucoadhesion of hydroxypropylmethacrylate nanoparticles to rat intestinal ileal segments in vitro.

The purpose of this study was to evaluate the adhesion of HPMA nanoparticles to mucus using a perfused rat ileum test system. Radiolabeled nanoparticles were prepared and deposited onto rat ileal segments in vitro. The segments were perfused and the perfusate was collected in fractions and assayed for radioactivity. Between 10 and 50% of the radioactivity was eliminated over the first 120-sec perfusion, whereas the remaining activity was firmly attached to the ileum. Among the variables tested, the time interval between nanoparticle deposition and perfusion played the major role, indicating that the mucus-nanoparticle interaction is likely to result from the diffusion of polymers into the mucus and of mucin into the polymeric matrix.

Simultaneous flow measurement of specific heats and thermal expansion coefficients of liquids: Aqueoust-BuOH mixtures and neat alkanols and alkanediols at 25C

A flow method is described for the simultaneous measurement of volumetric specific heat capacities cpv and thermal expansion coefficients α of liquids, using a Picker heat capacity microcalorimeter. the method involves a simple sequence of operations in which the calorimeter unit is used alternately to measure a difference in volumetric specific heats at constant flow rate and temperature, or a flow rate variation resulting from a temperature scan on a flow cell. The precision of the method in α measurements is close to 1% which is comparable to that of current dilatometric methods; the overall time for the combined cpv-α measurement is less than 30 minutes. Typical uses and reliability of the method are illustrated through results for aqueous NaCl solutions, t-BuOH-water mixtures, and α,ω-diols (C2−C5) at 25°C. The α and cpv values in homologous series of normal alkanes, alcohols and diols appear well represented by equations comprising two contributions, one related to the hydrocarbon chain length, the other dependent on the number density of −OH groups. The general trends in these data and comparison with similar results for H2O2 and H2O illustrate the magnitude of the cpv and α ‘anomalies’ in liquid water.