Force over four hour period

A series of small stresses were applied to a 0.03 M sample with an equilibrium 4-value of 183 A, reducing the 4-value to 143 A over a period of about four hours. A larger stress was then applied, and the gel was allowed to come to equilibrium with the applied stress for 15 hours. The 4-value is plotted as a function of time in Figure 3.2. After 2 hours the 4-value was 118 A, and after 15 hours when the curve has obviously flattened out, the 4-value was 115 A. In the available neutron beam time, it was not possible to allow the gel to come fully to equilibrium with each applied stress. An equilibration time of two hours was chosen. After this time the voltage was always steady to two significant figures, and we may surmise that the error of approximately 3 A introduced into the 4-spacing is an absolute one, which does not affect the shape of the measured force-distance curve. 

Over the four hour time period, the force produced can be seen to follow the oscillating reaction very closely, indicating that the diffusion through the gel is still quite fast relative to the timescale of the oscillations. The maximum force produced by the gel is 0.012N. The slight upward drift in the data is due to an increase in mass caused by a small mismatch between the flow rates of the pumps used. 

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