Nanoscale Investigation into Dynamics of Thin Liquid Films during Bouncing and Attachment of Rising Air Bubbles on Hydrophilic and Hydrophobic Surfaces.

Investigations on bouncing and attachment of free-rising air bubbles on hydrophobic surfaces have been limited to side-view, high-speed photography of the bubble-plate attachment process. In this work, an investigation of the dynamics as well as stability of thin liquid films (TLFs) between free-rising air bubbles and quartz surfaces was performed using a newly developed multiple-wavelength synchronized reflection interferometry microscopy (SRIM) technique. The effect of surface hydrophobicity on both the stability and critical rupture thickness of TLFs was investigated. Results showed that the TLF ruptured at a critical rupture thickness of 100-1000 nm or beyond during bubble's impact on hydrophobic quartz surfaces. The critical rupture thicknesses varied depending on the surface hydrophobicity as well as surface asperity. A higher surface hydrophobicity, in general, contributed to a higher critical rupture thickness. In addition, the effect of n-octanol on the stability of the TLFs was investigated. Results showed that film stability increased with increasing the concentration of n-octanol, which was accompanied by a significant decrease in the critical rupture thickness. The present result illustrates, for the first time, the dynamics of TLFs on hydrophobic surfaces under a dynamic condition compared with previous studies under a quasi-equilibrium condition. The information revealed from the present work has a significant implication to many industrial applications, including froth flotation and other biological and semiconductor applications.

Surface Forces in the Thin Liquid Films (TLFs) of Water Confined between n-Alkane Drops and Hydrophobic Gold Surfaces.

In flotation, air bubbles are commonly used to selectively collect the hydrophobic particles suspended in water, with the collection efficiencies strongly affected by contact angles and the properties of wetting films. Knowing that oil drops form substantially larger contact angles than air bubbles on a hydrophobic surface, many investigators explored the possibility of using oil drops rather than air bubbles for flotation. In the present work, the surface forces present in the thin liquid films (TLFs) of water confined between n-alkanes of different chain lengths and thiol-coated gold surfaces have been measured to better understand the drop-surface interactions, which are controlled by surface forces. The force measurements are conducted by monitoring the changes of local curvatures as an oil drop approaches a flat surface slowly, while monitoring film thicknesses by microinterferometry, constructing spatiotemporal film profiles, and analyzing the profiles to derive disjoining pressure and free energy isotherms using the Frumkin-Derjaguin isotherm. The results show that drop-hydrophobic surface interactions are driven by the hydrophobic force, which was first measured by Israelachvili and Pashley in 1982, and that both short- and long-range hydrophobic forces increase with contact angle and decrease with the chain lengths of n-alkane oils. It has been found also that the hydrophobic forces measured with oil drops have longer decay lengths than those measured with air bubbles, which may provide a kinetic advantage over the method of using air bubbles for flotation.

Effects of protein sources for milk replacers on growth performance and serum biochemical indexes of suckling calves.

This study investigated the effects of protein sources for milk replacers on growth performance and serum biochemical indexes of suckling calves. Fifty Chinese Holstein bull calves with similar BW and age were randomly allocated to 5 groups (1 control and 4 treatments) of 10 calves in each group. Five types of milk replacers were designed to have the same level of energy and protein. The protein source for milk replacers of the control group was full milk protein (MP). The protein source of milk replacers of the 4 treatment groups was composed of MP and one vegetable protein (VP) (30 and 70% of total protein). The 4 types of VP were soybean protein concentrate (SP), hydrolyzed wheat protein (WP), peanut protein concentrate (PP), and rice protein isolate (RP). Results of the experiment showed: 1) there was no significant difference on average daily gain (ADG) and feed:gain ratio (F:G) among the MP, SP and RP groups (P > 0.05), whereas the ADG and F:G of the WP and PP groups were significantly lower compared with the MP group (P < 0.05); 2) there was not a significant difference in withers height, body length and heart girth among treatment groups compared with the MP group (P > 0.05). Thereby the 4 VP milk replacers had no adverse effects on body size of calves; 3) all groups showed no significant difference in the serum contents of urea nitrogen, total protein, albumin, globulin, ß-hydroxybutyrate, growth hormone, insulin-like growth factor-1, and the ratio of albumin to globulin (A:G) (P > 0.05). In conclusion, SP or RP (accounts for 70% of the total protein) as calf milk replacers could substitute MP, whereas wheat gluten and PP had a significant adverse effect on growth performance in this experiment.