Liquidlike state

Fig. XII-12. Top friction traces for two calcium alkylbenzenesulfonate monolayers on mica where the monolayers are in a liquidlike state. A—in inert air atmosphere B—in saturated decane vapor. Bottom contact radius-load curves showing adhesion energy measured under the same conditions as the friction traces. (From Ref. 53.)...

When estimating air-aerosol partitioning of gas phase substances such as PAHs, most of which are solids, it is usual to use the liquid state vapor pressure as the correlating parameter. This is because the PAH is effectively in a liquidlike state on or in the aerosol particle. It does not exist in crystalline form. 

From these measurements it follows that the solvent molecules are in a liquidlike state even below glass temperature. This indicates that the solvent molecules are mobile within the numerous cavities of the polymer as in a liquid. With decreasing temperature more and more of them are fixed against each other and against the chain segments, until finally all plasticizer molecules are immobilized. 

Scientists have been aware of the novel properties of supercritical fluids for more than a century. Early investigators were fascinated by the schizophrenic behavior of this gaslike, liquidlike state, and it is disconcerting but coincidental that research activities also split into two disparate areas. Fundamental interactions in simple systems were meticulously investigated to correlate and predict phase behavior. At the other extreme, scientists applied supercritical fluids with Edisonian zeal, seeking miraculous solutions to complex problems in extraction and fractionation. 

The aggregates tend to overlap at high concentration. While the system remains in a liquidlike state, the apparent diffusion constant decreases. The structural features obtained by comparison of static and dynamic data are not accessible solely by one technique [63]. 

An interesting property of many polymers is their ability to undergo a temperature dependent transition from a primarily liquidlike state (sol) to a gel possessing elasticity. The temperature at which this transition occurs is termed the sol-gel transition. Given the relevance of this transition to both the clinical and nonclinical performance of pharmaceutical systems, various authors have examined this phenomenon using thermoanalytical methods, including thermal oscillatory analysis. Examples of these are now presented. 

Regarding local molecular dynamics, it is well established that all surfactant self-assemblies are characterized by very rapid short-range dynamics. The surfactant chains, as well as oil and water molecules, are in a liquidlike state. Local molecular reorientation occurs on time scales of 10 s, similar to pure water or hydrocarbon. On the other hand, due to the presence of the surfactant films, the reorientation is more or less anisotropic. Local translational motion is also quite fast, but long-range translation is strongly dependent on the presence of the surfactant films. 

The preceding qualitative observations about the temperature dependence of and Vg — V, can be extended to a quantitative statemem in cases for which thie effective molecular volume of the penetrant in the sorbed state can be estimated. As a first approximation, one may assume that the effective molecular volume of a sorbed CO2 molecule is 80 A in the range of temperatures from 25 to 85 C. This molecular volume corresponds to an effective molar volume of 49 cmVmol of CO molecules and b similar to the partial molar volume of CO in various solvents, in several zeolite environments, and even as a pure subcritical liquid (see Tables 20.4-4 and 20.4-5). The implication here is not that more than one CO molecule exists in each molecular-scale gap, but rather that the effective volume occupied by a CO molecule b roughly the same in the polymer sorbed state, in a saturated zeolite sorbed state, and even in a dissolved or liquidlike state since all these volume estimates tend to be similar for materials that are not too much above their critical temperatures. With the above approximation, the predictive expression given below for Ch can be compared to independently measured values for this parameter from sorption measurements ... 

Author of this article has made an attempt to extend further our notions of liquid [11,12]. It is considered now that sublimation is a direct transition from solid (crystalline) state of matter into gas. The author has propounded and substantiated the principle of least time for first-order phase transitions [11,13] it is shown by means of this principle that sublimation goes in two steps through a certain intermediate state in the form of surface film. It is concluded that this film consists of nonstructural liquidlike substance which is a certain antipode of liquid this liquidlike state of matter is named second licjuid [12]. 

Once the film has transformed to a glassy state, it behaves like a solid. The response to small shear stresses is elastic (Figure 6). Above a yield stress the film rearranges and flows. In some cases the film enters a liquidlike state (15,16), and in others it cracks at the wall or in the center of the film and shears along the resulting interface. The two situations are difficult to identify in experiments, which do not yet provide direct structural information. 

In the solid state the poly(L-lysine)-dodecylsulfate complex is invariably organized in a lamellar stmcture consisting of layers of polypeptide chains alternating with double layers of surfactant molecules arranged tail to tail. However, both the secondary structure adopted by the polypeptide and the packing of the polymethylene chains in the paraffinic phase depend upon the history of the sample. In the powder isolated from synthesis, the structure of the complex is predominantly of P-sheet with sidechains in a liquidlike state characterized by only short-range order. On the contrary, films cast from a chloroform solution in which the polypeptide is in the disordered state exhibit an a-helix conformation of the mainchain with sidechains also uncrystallized but with the mobility more restricted than in the former case. 

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