Much attention has been given to the subject of structure of Liquids, but it may be safely said that every theory advanced as far, while holding good for a limited number of liquids ever a limited range of temperature, suffers in one respect or in other. In this way, there is no even moderately satisfactory theory accounting for the behaviour of various important physical and thermo dynamical properties of liquids. One of the main reason for their setback is the non-availability of sufficient date for a good number of liquids, accurate to the required degree and ever a considerable range of temperature. Thus, for a more consistent and coherent theory regarding the aggregate formation of the molecules and their mutual forces, not only a thorough investigation of various properties for a number of liquids is required, but also, their behaviour over a reasonable range of temperature is to be determined. To contribute in this direction, a fresh approach, which is essentially a differential one, is made by undertaking a series of experiments for a number of liquids and solutions in the present work. Three important properties namely, viscosity, refractive index and dilatation have been examined, and general inferences are drawn by making a critical analysis of these data. It opens up a new field of investigations, and the characteristic features which may keep this work distinguishable are ,(i) consistent improvement of the experimental accuracy to the required specifications, (ii) making extensive studies on a good number of liquids bearing importance from the structural view point, and (iii) experimentation on various properties over a considerable range of temperature, and at comparatively smaller thermal intervals. Naturally, the subject matter has been mainly divided into three related parts, each being based and developing from other one, and devoted to a detailed examinations of respective studies that have been made on each of these properties.
Part I of these investigations contains the experiments which describe the results of measurements that have been carried out to examine the influence of straight-chain hydrocarbons used as diluents for simple aromatic compounds and non associated liquids. A brief account of the work carried out previously on this topic, and the measuring procedure is given in the Chapter I covering the survey of the previous work and experimental technique of these studies. Chapter II deals with the viscosity determinations and the depression due to the interaction of various components, each being treated with the corresponding appropriate hydrocarbon, while Chapter III comprises similar results obtained on phenol and xylenes, together with the studies on some non-associated liquids, well knows for their structural simplicity. In order to maintain the necessary and sufficient balance of viscosity , density and volatility of the two components of the mixture, as well as to confirm the reproducibility of the phenomena, each of the liquid is studied by mixing it with two different hydrocarbons, and the overall mean values for the final results are adopted. For all the systems investigated, the estimates for excess free energies of mixing delta Gm are obtained from the corresponding data of maximum values of the relative viscosity depression, and their temperature variations are provided graphically. It is concluded that, (i) the viscosity depression is dependent only upon the actual viscosity and miscibility of the system, (ii) the delta Gm values undergo a non-uniform temperature variation showing the segments or steps, and (iii)the observed segments or steps become more clear and defined with the improvement of the experimental methodology and by reduction in the measuring interval delta T. For the mixtures hepten/non case with benzene. It can be inferred that the viscosity depression of benzene signifies the polar interaction of benzene nucleus in the solution, as the consequence of the residual intermolecular forces emanating from the resonating electrons of benzene ring. Thus it suggest, that viscosity depression can be explained in terms of benzene-benzene interaction replaced by benzene-nonane and benzene-heptane. Moreover, a comparison of the deduced free energies of mixing of different system is made with that of benzene, and the general values for various series are obtained.
Since as a consequences, the refined measurement on viscosity lead to the determination of motivation energy of viscous flow E, such studies are next described in the Part II of the present measurements . After providing a brief account of the previous work and measuring procedure. Which is essentially a differential one and based on the well known Andrade’s question (i), a detailed examination is made of straight-chain aliphatio hydrocarbons from C6 to C12 and of some mineral oils. It is observed that these hydrocarbons exhibit step-like structure for the temperature variation of E at lower temperature , which ultimately changes over to sinsoidal fluctuation at a worked temperature well below their boiling point. This transaction temperature being the specific characteristic of the straight chain hydrocarbons and varies in a regular manner with the number of carbonatous in the chain-length. An attempt is made to apply existence of instable equilibrium position in the energy levels of liquids, and it is found that the knowledge of transition temperature yields valuable information regarding the aggregate formations in the liquid, the flow unit in the chain, the average chain-length and the heat of vagorization It provides letter and accurate results and prove to be more convenient than the corresponding generally adopted plot of extrapolated heat of vagorization
Ffor the reasons of the existence of hydrogen bonding , the studies on hydroxylic liquids had been of special interest in these laboratories, hence an intensified effort is made is the subsequent series of work to examine the aqueous ethanol solutions, both concentrated and dilutes. Chapter VI contains an extensive series of experiments on the concentrated ethanol solutions performed at the smaller concentration intervals, covering the whole range of 4% to 34% water. It is observed that while E undergoes cyclic fluctuations, the positions and the magnitudes of the peaks vary in a systematic manner with alcohol contest. An interesting correlation is noticed between the peak position and ethanol concentration as the minima show a series of smooth and regular progressions for the contiguous concentrations, which are frequently observed to branch out. At the critical concentration of 34.5% water, the sinusoidal character becomes negligible to such an extent that the phenomenon could be considered to becomes the segmental or step like structure. Evidently, these fact these facts are attributable to the occurrence of some remarkable structural changes in the solutions, corresponding to various modes of peaks variations. The subsequent chapter covers the measurements extended to the dilute ethanol solution, carried out from 0% to 24% alcohol and at intervals of 0.6% ethanol. These experiments not only confirm the existence of the sharp jumps between the successive sets of constant values of the activation energy of viscous flow on firmer basis, but further establish the dependence of the position and magnitude of these transition on the temperature and the concentration. The discontinuities or jumps are classified as “large”, “medium” or “small”, compared with mean values of (Delta E/R)/1000=0.07, and a plot for their position is obtained (Fig.VII.5) by utilizing the total available data. Here again, the possible course traced out by the jumps is obtained by linking all these points together as a series of progressions, most of them showing a smooth movement. In some regions, particularly below 6% water these progressions like those of the concentrated solutions frequently branch out, thus indicating the complex nature of phenomena connected with the changes. These characteristic phenomena are associated with the occurrence of sudden, discontinuous and abrupt type of structural changes in the molecular aggregates and their energy levels near 0% alcohol (water), hence indicating the distortion of OH linked polyhedra in water even by the addition of small quantity of othanol.
For further elucidation. It was considered necessary to investigate the nature of the energy jumps and their inherent with, by carrying out the measurements at comparatively closely spaced temperature intervals of 0.2 C to 0.5o.C .Some remarkable jumps previously found in water and dilute solutions of alcohol are re-examined ,and the results thus obtained lead to the conclusion that the natural inherent with of these transitions lies within the limits of the experimental interval. This provides an overwhelming evidence for the real existence of the second order transitions occurring on these discontinuities, is the second or third derivatives of Gibb”s function like those of paramagnetism ferromagnetism of B brass alloy.
To further the order of the transition it was considered highly instructive to investigate the other related physical properties such as dilatation and refractive index. The part III of the present work contains a detailed examination of refractometric measurements, made on liquids and solutions by using Pulfrich critical angle instrument. The experiments on ethanol solutions with concentration, those found in the other extreme of the system undergo a fascinating process of amplitude variation, as some of them are completely annihilated at the characteristic concentrations. Here again, the occurrence of the anomalous branching out of of the progressions for the variation of the minima with concentration near 0% ethanol further confirms on the sounder footing the existence of the important structural changes taking place in these solutions. Further more, the phenomenon of the variation of the peak which does not undergoes a significant change with alcohol content upto 0.8%% ethanol provides a fresh interpretation for the persistence of water type structure in very dilute solutions in accordance with the current ideas on the chemistry of water.
Lastly, some poly alcohols, benzene and hexane were subjected to similar refractometric determinations (Chapter X). For amly alcohol, isoamyl alcohol and butyl alcohol it was noticed, that the minima and the maxima occurring in the refractometric measurements have their counterpart in those of the discontinuities observed in the activation energy of viscous flow, thus establishing a definite correspondence between these two different phenomena studied. Similarly, one-to-one correspondence is observed for benzene and hexane as well, and it is further noticed that the temperature position of the minima in –(dn/dt)exceeds over those for the transitions in E by about one-quarter of their respective mean cyclic period, which according to the Dal”s law indicates that the sinusoidal variation observed in these liquids may be connected with the corresponding changes in the polarization.