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Structure and phase diagram of an adhesive colloidal dispersion under high pressure: A small angle neutron scattering, diffusing wave spectroscopy, and light scattering study
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic phase diagram of adhesive hard sphere system. Shown is the action of pressure on the loci of coexistence and percolation lines. The observed temperature shift under the action of 1 kbar pressure amounts to about .

Image of FIG. 2.
FIG. 2.

Theoretical phase diagram of an adhesive hard sphere model taken from Fantoni et al. (Ref. 35. Their new data (dotted lines) is denoted as PY and is in this plot compared to MC simulations from Miller and Frenkel (Ref. 7) which are shown as full lines and filled squares. Dashed lines denote the model C1 according to Fantoni et al. (Ref. 35). In this model, the value for is to a good approximation given by Eq. (7).

Image of FIG. 3.
FIG. 3.

(a) The transition is determined by the pressure at which the correlation functions clearly deviate from a narrowly distributed CONTIN distribution. Here as an example measurements at . The single exponential decay gives a narrow CONTIN peak, top at , and broadening indicating crossing the coexistence, middle at . Correlation function at the bottom at indicates a transition to the spinodal region. No CONTIN analysis possible. (b) Phase transition pressures at a volume fraction of as a function of temperature. The two straight lines in the figure have a slope of as determined by linear fits to the data.

Image of FIG. 4.
FIG. 4.

Normalized raw data of the two-cell DWS setup for a volume fraction of 16% is shown on the left side. On the right side, the same data are corrected for the decay of the second cell. With increasing pressure, the correlation functions decay at later lag times and eventually build up a plateau, which is a clear sign of a nonergodic state. Temperature of measurement is .

Image of FIG. 5.
FIG. 5.

The cumulant fit coefficient is corrected for multiple scattering and plotted against pressure at a temperature of measurement of . The arrows indicate the first nonergodic file measured as described in Sec. III C. The samples with a volume fractions of 1% and 5% remain ergodic.

Image of FIG. 6.
FIG. 6.

vs for different volume fractions (top: 5%, 11.2%, and 39.2%; bottom: 16%) and temperatures as given in the figures (plotted with an offset). In each data set the pressure is varied and values are indicated in the figures. Full lines are calculated according to Eq. (13) with according to Ref. 18. The was calculated on the basis of the Robertus model with sticky hard sphere interactions. Deviations of fit from data at intermediate are due to not taking the experimental resolution into account. This was proven not to influence the analysis of the stickiness at small . For details of fit see text.

Image of FIG. 7.
FIG. 7.

Plot of inverse stickiness vs pressure calculated from parameters of the global fit for volume fraction 16% using Eq. (6).

Image of FIG. 8.
FIG. 8.

The forward intensity plotted vs the reduced pressure according to Eq. (16). We used for the SANS data (filled circles) and LS (filled triangles) at . SANS data (filled squares) at and with [pressure value from Fig. 3(b)]. The straight line through the data points has the slope of −1 suggesting a mean field type of behavior. All curves are vertically shifted to the SANS data to show the general critical behavior irrespective of the chosen temperature of measurement. The other, steeper straight line shown in the figure has a slope of −1.24, which would correspond to a scaling behavior of the 3D Ising case. Clearly, our data are not in agreement with this expectation.

Image of FIG. 9.
FIG. 9.

The relaxation rates divided by vs the reduced pressure for the 5, 11, and 16% samples at . The straight line has the slope of 1 suggesting mean field type of behavior. We have used the value for the critical pressure of from , as deduced from Fig. 3(b). The same was used in Fig. 8. From the measured transmissions of our samples we have then determined the transmission at the sample at that pressure and have used this value to determine the for the sample.

Image of FIG. 10.
FIG. 10.

Final experimental phase diagram. Lines are guides to the eye. Dotted line: DWS coexistence line. Solid line: DWS percolation line. Dashed line: SANS percolation line. The phrase “visual inspection” in the inset refers to the phase diagram given in Ref. 18. All other symbols are explained in the inset.

Image of FIG. 11.
FIG. 11.

Comparison between theoretical phase diagram and our data (triangles). Data are converted into temperature using our global fit parameters and Eq. (6). Also shown is simulated percolation data from Kranendonk et al. (Ref. 6) and Seaton and Glandt (Ref. 5). MC is data from Miller and Frenkel (Ref. 7) which is similar to the data of Fantoni et al. (Ref. 35, see Fig. 2). The PY model is given by Eqs. (7) and (8), respectively.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Structure and phase diagram of an adhesive colloidal dispersion under high pressure: A small angle neutron scattering, diffusing wave spectroscopy, and light scattering study