Forcing loops

Figure 26.9 A typical Wilhelmy force loop of a relatively hydrophobic surface the force loop is composed of three cycles each consisting of one immersion (advancing) and one emersion (receding) process. The sample plate is polycarbonate (PC) modified with TMS plasma.

Figure 26.11]. This is a result of the strong adhesive forces due to the strong interactions of the high-energy surface and water molecules. The three-phase contact line starts to advance toward the dry surface (b c) immediately after contact is made with the water. In this case, the two-stage line (A C) in Figure 26.9 appears as a straight line as in the force loops of (TMS-I-02)-treated polymers depicted in Figure 26.12.

Figure 26.13 The effects of plasma treatment on wettability, which is given by the cosine of the dynamic advancing contact angles, cos 0d calculated from the first immersion FjL lines of each force loop dotted lines indicate the mean cos 0D,a,i of TMS and TMS+O2 treated polymers.

The force loop for untreated samples are shown in Figure 26.14. The force loops for TMS plasma-treated and (TMS O2) plasma-treated surfaces are shown in Figure 26.15. Any sign of deviation from the parallelogram force loop is an indication of surface dynamic instability. Plasma polymerization coating of (TMS O2) seems to cause some degree of surface dynamical instability depending on the nature of substrate polymer, e.g., PTFE, UHMWPE, HDPE, and PMMA. 

Figure 26.14 Force loops of the following untreated conventional polymer plates A) PTFE, B) UHMWPE, C) PP, D) LDPE, E) HDPE, F) PC, G) PET, H) PMMA, I) PVDF, J) nylon dotted lines indicate the surface tension of water, force loops were generated by a constant immersion/emersion rate of 5mm/min.

Figure 26.18 Rows A and B correspond to the force loops of the following glass slide dimensions (A) H = 25.4mm, L = 1 mm, (B) H = 22 mm, L = 0.153 mm. Each column from 1 to 3 correspond to the following plasma treatments (1) TMS treated, (2) (TMS + O2) treatment (O2/TMS = 4), (3) O2 treatment. The dotted lines correspond to the surface tension of water, and the dashed lines correspond to the ceiling buoyancy of the plate immersed to 7.5 mm depth.

WILHELMY FORCE LOOPS AND FLUID HOLDING TIME... 

Figure 26.22 Wetting stages of Wilhelmy force loops on a polymeric plate the gray and black lines depict the absence and presence of a continuous water film, respectively the consecutive wetting stages of a Wilhelmy force loop are as follows (A) first immersion (Adv.l), B) first emersion (Rec.l), (C) second immersion (Adv.2), and D) second emersion (Rec.2).

Three different cases of aqueous film stability indicated by FHT are depicted in Figure 26.23. Corresponding force loops and diagrams of the continuous water film... 

Figure 26.23 Interpretation of fluid holding phenomena on vertical plates immersed in solution to a depth of 15 mm (indicated by the dotted line on each plate) and then raised to a depth of 5 mm corresponding force loop plots with fluid holding times of (A) 0 s, (B) 57 s, and (C) 115s were calculated from a constant immersion speed of 300 mm/s.

Wilhelmy plate wetting parameters, such as plate velocity during immersion or emersion and halting the motion of the plate after immersion or emersion, have been shown to alfect the intrinsic hysteresis, which consequently affects the overall shape of the force loop [3]. These wetting parameters were found to affect FHT differently depending on whether pure water or an aqueous artificial tear solution was employed as the wetting medium. 

The effect of first emersion velocity on force loop shape is shown in Figure 26.26. The force loops for tear fluid behave independently from the first emersion velocity, since the second immersion velocity is fixed in this case. Therefore, the tear fluid FHT is constant, as depicted in Figure 26.27. 

Figure 26.24 Wilhelmy force loops of (CH4 + air) plasma treated glass plates in (W) DDI water and (T) artificial tear fluid at varying second immersion velocities (1) 2mm/min, (2) 5mm/min, (3) lOmm/min, and (4) 20mm/min. Plasma discharge conditions were 38W, SOmTorr, 1 seem CH4, 2 seem air, 20 min first and second emersion and first immersion velocities were fixed at 20mm/min, the use of water and tear fluid 4elded advancing contact angles, 0D,a,i means, and standard deviations of 47° 1 and 48° 3, respectively.

Figure 26.30 Wilhelmy force loops of (A) nylon-6, (B) PMMA, and (C) PTFE plates in artificial tear solution. At the end of the first emersion, the plates were held out of the solution for (1) Omin, (2) 5 min, and (3) 40 min at a depth of 5 mm the use of tear fluid on nylon-6, PMMA, and PTFE, yielded advancing contact angles, 0D,a,i. means, and standard deviations of 68° 3, 91° 3, and 130° 1, respectively.

Figure 26.31 Wilhelmy force loops of (A) untreated, (B) (CH4 + air) plasma treated, and (C) (CH4 + air) plasma then O2 plasma treated contact lens material using artificial tear fluid the emersion/immersion velocities were all fixed at 5 mm/min.

Figure 30.1 Comparison of Wilhelmy force loops (a) LDPE, (b) O2 plasma-treated LDPE.

Figure 30.2 Correlation between the overshooting in Wilhelmy force loop and the plasma susceptibility expressed by the weight loss rates.

Figure 30.3 The effects of O2 flow rate and the treatment time on Wilhelmy force loop Column A 1 seem, B 10 seem, Row from top (1) 0.2 min, (2) 1 min, (3) 2 min, (4) 4 min. System pressure and input power were fixed at SOmtorr and 36 W respectively. The dynamic advancing contact angle of water and fluid holding time, FHT, are shown on each plot.

Figure 30.5 The effects of input power (A) 8 W, (B) 30 W, (C) 63 W, and system pressure (1) 25mtorr, (2) 50mtorr, (3) lOOmtorr, on Wilhelmy force loops of O2 plasma-treated LDPE oxygen flow rate and plasma treatment time were fixed at 10 seem and 0.2 min, respectively, dark-colored force loops were taken just after samples were removed from the reactor, and gray-colored force loops were taken two weeks later after equilibrating with ambient air.

Online, force-loop-feedback systems are used for weight control on most production tablet presses. Upper and lower punch forces as well as mean punch force can be monitored by load cells for each station on the tablet press. Deviations between the target and actual compaction forces are measured, and adjustments to the punch filling depth are automatically made to bring the mean force back into the target range. In some cases, the speed of the force feeders on the press is adjusted by reducing the observed variability of the compression force data. 

LAS acid neutralization can be performed by means of a process unit based on the principle of the forced loop [11] in which the reactants are continuously dosed and the heat of reaction is immediately dispersed over the mass of neutralized product kept under recycling. 

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