Studies on the Surface Properties of Alcohol Ethoxylate and the Application in Suspension Concentrate†

doi:10.7503/cjcu20140331

Abstract

Abstract:

The paper studies the critical micelle concentration(cmc), the equilibrium surface tension(γ_cmc), the standard free energy of micellization(ΔG_m), the area per molecular at cmc(A_cmc) and hydrophile lipophile balance(HLB), which are affected by the function of the oxyethylene group(EO) number in the alcohol ethoxylate(AEO). It also studies the influence of AEO with different EO number as dispersants on the rheological properties(viscosity, storage modulus G', γ_flow and thixotropy) and the physical stability(the suspension rate before and after the hot storage, residual pourability ratio) of Mancozeb(25%) suspension concentrate(SC). As the value of the oxyethylene group number increase from 4 to 20, the values of cmc, γ_cmc, ΔG_m, A_cmc and HLB are rising. The adding of AEO can reduce the viscosity of Mancozeb(25%) SC, and the SC with AEO-9 has the lowest viscosity. With the increase of the EO chains in AEO, the thixotropy recovery of SC which has higher residual pourability ratio decreases gradually. Through strain sweep, we find the values of G' and γ_flow reflect the structural variation of the SC, and then G' and γ_flowcan be used as suitable SC stability indicators.

Key words: Alcohol ethoxylate, Surface property, Suspension concentrate, Rheology

CLC Number:

O648

TrendMD:

QIN Jiaolong, PANG Wenwen, YANG Xiaodong, ZHANG Teng, REN Tianrui. Studies on the Surface Properties of Alcohol Ethoxylate and the Application in Suspension Concentrate^†[J]. Chem. J. Chinese Universities, 2014, 35(10): 2182.

Figures/Tables 17

Fig.1 Surface tension γ plotted as a function of concentration of AEOs

Table 1 Surface and micellar properties of AEO surfactants obtained in aqueous solution*

No.	γ_cmc/(mN·m^-1)	10⁵cmc/(mol·L^-1)	A_cmc/(nm²·molecule^-1)	ΔG_m/(kJ·mol^-1)	HLB
AEO-4	25.80	3.79	0.601	-25.14	9.96
AEO-7	26.80	4.63	0.941	-24.74	12.55
AEO-9	29.10	6.52	0.956	-23.89	13.49
AEO-15	37.50	7.86	0.960	-23.43	15.16
AEO-20	41.90	8.44	1.266	-23.25	15.69

Fig.2 Effects of EO number on cmc and γcmc at 25 ℃

Fig.3 Effects of EO number on Acmc and ΔGm at 25 ℃

Fig.4 Flow curves for AEO-SCs at 25 ℃ ● SC; ○ SC-AEO-4; ■ SC-AEO-7; ▼ SC-AEO-9;□ SC-AEO-15; Δ SC-AEO-20.

Fig.5 Viscosity curves for different AEO-SCs at constant shear rate(10 s-1) ● SC; ▽ SC-AEO-4; ◆ SC-AEO-7; □ SC-AEO-9;■ SC-AEO-15; ◇ SC-AEO-20.

Fig.6 Viscosity curves for different AEO-SCs at constant shear rate(100 s-1) ● SC; ○ SC-AEO-4; ■ SC-AEO-7; ▼ SC-AEO-9;□ SC-AEO-15; Δ SC-AEO-20.

Fig.7 FESEM images of SC(A) and SC-AEO-9(B)

Table 2 Rheological parameters of SC-AEOs

Sample	Bingham model				Herschel-Bulkley model
Sample	τ₀/Pa	η_P/(Pa·s)	R²	n	K/(Pa·sⁿ)	τ₀/Pa	R²
SC	18.22	0.0227	0.9458	1.1489	0.009358	18.47	0.9468
SC-AEO-4	8.967	0.01184	0.9945	0.8802	0.02433	8.828	0.9970
SC-AEO-7	1.2806	0.0302	0.9458	0.6507	0.2238	0.3696	0.9999
SC-AEO-9	0.8827	0.02191	0.9487	0.6551	0.1575	0.2436	0.9999
SC-AEO-15	2.8473	0.02439	0.9692	0.7128	0.1317	2.176	0.9982
SC-AEO-20	1.3026	0.02536	0.9498	0.6385	0.2040	0.4668	0.9999

Table 3 Stability analysis of SC-AEOs

Ssmple	W₁(%)	W₂(%)	S_t	τ₀/Pa	τ_flow/Pa	γ_flow(%)
SC	30.00	25.00	813.5	18.47	18.47	2.492
SC-AEO-4	94.55	91.05	745.6	8.828	2.228	29.09
SC-AEO-7	95.92	94.57	12.24	0.3696	0.2967	10.59
SC-AEO-9	94.42	96.12	11.12	0.2436	0.2286	13.46
SC-AEO-15	94.89	94.47	89.23	2.176	0.7787	27.70
SC-AEO-20	95.01	95.81	18.41	0.4668	0.6075	23.31

Fig.8 Dependence of the elastic modulus(G') on strain amplitude(γ) ● SC; ○ SC-AEO-4; ■ SC-AEO-7; ▼ SC-AEO-9;□ SC-AEO-15; Δ SC-AEO-20.

Fig.9 Strain sweep experiment of SC-AEOs ●○ SC; ▼▽ SC-AEO-4; ▲Δ SC-AEO-4;◆◇ SC-AEO-7; ■□ SC-AEO-9.G': solid circle; G″: hollow circle.

Table 4 Rheological data of three interval thixotropy and residual pourability test

Sample	Structure recovery ratio(%)				R(%)
Sample	5 s		7 s	10 s	15 s
SC	113.9	111.4	112.2	111.7	≥20
SC-AEO-4	76.69	83.84	91.68	99.07	10
SC-AEO-7	54.92	60.06	64.37	68.78	7
SC-AEO-9	44.26	49.70	54.05	58.41	≤5
SC-AEO-15	27.91	31.41	35.06	38.75	≤3
SC-AEO-20	40.63	45.17	48.97	52.93	≤3

Fig.10 Three interval thixotropy curves of SC-AEOs ● SC; ○ SC-AEO-4; ■ SC-AEO-7; ◇ SC-AEO-9;◆ SC-AEO-15; Δ SC-AEO-20.

Fig.11 Conformation of AEO-4(A), AEO-9(B) and AEO-20(C)

Fig.12 Effect of AEOs with different EO chains on dispersion ability of particles (A) Short or no AEO: flocculation; (B) proper EO chains: dispersion; (C) too long EO chains: bridging.

Fig.13 Illustration of the effect of AEOs (A) Without dispersant or AEO with short EO chain as dispersant; (B) AEO with long EO chain as dispersant.

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